diff --git a/.changeset/bottom-sheet-replace-aligns.md b/.changeset/bottom-sheet-replace-aligns.md
new file mode 100644
index 0000000000000..161323f07f295
--- /dev/null
+++ b/.changeset/bottom-sheet-replace-aligns.md
@@ -0,0 +1,7 @@
+---
+'@astryxdesign/core': patch
+---
+
+[fix] When one standalone `BottomSheet` replaces another and the entering sheet is shorter, the sheet being replaced moves down to the entering sheet's top edge while the entering sheet rises, and only then fades, so the switch reads as one sheet changing height, as a `BottomSheetSwitcher` step change does. It had stayed at its own height and faded out above the entering sheet. Under reduced motion the replaced sheet still does not move.
+
+@imdreamrunner
diff --git a/packages/core/src/BottomSheet/BottomSheetReplace.test.tsx b/packages/core/src/BottomSheet/BottomSheetReplace.test.tsx
index 28967e0403eb9..4154094c1df05 100644
--- a/packages/core/src/BottomSheet/BottomSheetReplace.test.tsx
+++ b/packages/core/src/BottomSheet/BottomSheetReplace.test.tsx
@@ -170,6 +170,58 @@ function layout(element: HTMLElement, top: number, height: number) {
   element.getBoundingClientRect = () => new DOMRect(0, top, 390, height);
 }
 
+/**
+ * Lay out a standalone step as the browser does: its dialog spans the
+ * viewport and its panel sits directly in it, `top` from the viewport top.
+ * Nothing between them marks where the panel rests.
+ */
+function layoutSheet(dialog: HTMLElement, top: number, height: number) {
+  layout(dialog, 0, 844);
+  layout(getPanel(dialog), top, height);
+}
+
+/**
+ * Give a panel the computed transform a browser reports while it travels
+ * `offset` px below where it rests (an entrance in flight), with the matrix
+ * type the browser has and jsdom lacks. Returns the undo.
+ */
+function travel(panel: HTMLElement, offset: number): () => void {
+  const view = panel.ownerDocument.defaultView as Window & {
+    DOMMatrixReadOnly?: unknown;
+  };
+  class Matrix {
+    m42: number;
+    constructor(transform: string) {
+      const values = /^matrix\((.*)\)$/.exec(transform)?.[1].split(',') ?? [];
+      this.m42 = Number(values[5] ?? 0);
+    }
+  }
+  const hadMatrix = 'DOMMatrixReadOnly' in view;
+  const previousMatrix = view.DOMMatrixReadOnly;
+  view.DOMMatrixReadOnly = Matrix;
+  const getComputedStyle = view.getComputedStyle.bind(view);
+  const spy = vi
+    .spyOn(view, 'getComputedStyle')
+    .mockImplementation((element, pseudo) => {
+      const style = getComputedStyle(element, pseudo);
+      if (element === panel) {
+        // Each call returns a fresh declaration; shadow its `transform`.
+        Object.defineProperty(style, 'transform', {
+          value: `matrix(1, 0, 0, 1, 0, ${offset})`,
+        });
+      }
+      return style;
+    });
+  return () => {
+    spy.mockRestore();
+    if (hadMatrix) {
+      view.DOMMatrixReadOnly = previousMatrix;
+    } else {
+      delete view.DOMMatrixReadOnly;
+    }
+  };
+}
+
 type Step = 'one' | 'two' | 'three' | null;
 
 /**
@@ -455,8 +507,8 @@ describe('BottomSheet replace: the handoff', () => {
     // Step one is 400px tall; step two will rest 160px lower. The panels are
     // mounted already, so lay them out before the switch: the alignment is
     // measured when the entering motion starts.
-    layout(getPanel(one), 444, 400);
-    layout(getPanel(two).parentElement as HTMLElement, 604, 240);
+    layoutSheet(one, 444, 400);
+    layoutSheet(two, 604, 240);
     fireEvent.click(screen.getByRole('button', {name: 'Continue to two'}));
     expect(summary()).toEqual(['One:replaced-aligning:0', 'Two:replacing:0']);
     expect(getPanel(one).style.transform).toBe('translateY(160px)');
@@ -474,8 +526,8 @@ describe('BottomSheet replace: the handoff', () => {
     openFlow();
     const one = getDialog('One');
     const two = getDialog('Two');
-    layout(getPanel(one), 444, 400);
-    layout(getPanel(two).parentElement as HTMLElement, 604, 240);
+    layoutSheet(one, 444, 400);
+    layoutSheet(two, 604, 240);
     fireEvent.click(screen.getByRole('button', {name: 'Continue to two'}));
     endMotion(one, 'transform');
     expect(summary()).toEqual(['One:replaced-aligning:0', 'Two:replacing:0']);
@@ -488,13 +540,55 @@ describe('BottomSheet replace: the handoff', () => {
     openFlow();
     const one = getDialog('One');
     const two = getDialog('Two');
-    layout(getPanel(one), 604, 240);
-    layout(getPanel(two).parentElement as HTMLElement, 444, 400);
+    layoutSheet(one, 604, 240);
+    layoutSheet(two, 444, 400);
     fireEvent.click(screen.getByRole('button', {name: 'Continue to two'}));
     expect(summary()).toEqual(['One:replaced-covered:0', 'Two:replacing:0']);
     expect(getPanel(one).style.transform).toBe('');
   });
 
+  it('aligns to where the entering sheet comes to rest, not where its entrance has it', () => {
+    render(<Flow />);
+    openFlow();
+    const one = getDialog('One');
+    const two = getDialog('Two');
+    layoutSheet(one, 444, 400);
+    // Two rests at 604 but is still 240px below that, rising.
+    layoutSheet(two, 844, 240);
+    const restore = travel(getPanel(two), 240);
+    try {
+      fireEvent.click(screen.getByRole('button', {name: 'Continue to two'}));
+    } finally {
+      restore();
+    }
+    expect(summary()).toEqual(['One:replaced-aligning:0', 'Two:replacing:0']);
+    expect(getPanel(one).style.transform).toBe('translateY(160px)');
+  });
+
+  it('moves the taller sheet back down when the person goes back to a shorter step', () => {
+    render(<Flow />);
+    openFlow();
+    fireEvent.click(screen.getByRole('button', {name: 'Continue to two'}));
+    endMotion(getDialog('Two'), 'transform');
+    endMotion(getDialog('One'), 'opacity');
+    fireEvent.click(screen.getByRole('button', {name: 'Continue to three'}));
+    endMotion(getDialog('Three'), 'transform');
+    endMotion(getDialog('Two'), 'opacity');
+    expect(summary()).toEqual(['Three:top:0']);
+    const two = getDialog('Two');
+    const three = getDialog('Three');
+    layoutSheet(three, 388, 456);
+    layoutSheet(two, 444, 400);
+    fireEvent.click(screen.getByRole('button', {name: 'Back to two'}));
+    expect(summary()).toEqual(['Three:replaced-aligning:0', 'Two:replacing:0']);
+    expect(getPanel(three).style.transform).toBe('translateY(56px)');
+    endMotion(two, 'transform');
+    endMotion(three, 'transform');
+    expect(summary()).toEqual(['Three:replaced-fading:0', 'Two:replacing:0']);
+    endMotion(three, 'opacity');
+    expect(summary()).toEqual(['Two:top:0']);
+  });
+
   it('keeps the scrim on the replaced sheet and hands it to the new sheet with no fade', () => {
     render(<Flow />);
     openFlow();
@@ -956,6 +1050,24 @@ describe('BottomSheet replace: reduced motion (design:reduced-motion)', () => {
     expect(openDialogs()).toEqual([]);
   });
 
+  it('the replaced sheet does not move down to a shorter entering sheet (DR1), and the handoff still ends after its fade', () => {
+    stubMedia(['(prefers-reduced-motion: reduce)']);
+    render(<Flow />);
+    openFlow();
+    const one = getDialog('One');
+    const two = getDialog('Two');
+    layoutSheet(one, 444, 400);
+    layoutSheet(two, 604, 240);
+    fireEvent.click(screen.getByRole('button', {name: 'Continue to two'}));
+    expect(summary()).toEqual(['One:replaced-aligning:0', 'Two:replacing:0']);
+    expect(getPanel(one).style.transform).toBe('');
+    endMotion(two, 'transform');
+    endMotion(one, 'transform');
+    expect(summary()).toEqual(['One:replaced-fading:0', 'Two:replacing:0']);
+    endMotion(one, 'opacity');
+    expect(summary()).toEqual(['Two:top:0']);
+  });
+
   it('fine pointer (DR3): an exit ends on its (collapsed) transform, as without the preference', () => {
     stubMedia(['(prefers-reduced-motion: reduce)']);
     render(<Flow />);
diff --git a/packages/core/src/BottomSheet/bottomSheetStack.ts b/packages/core/src/BottomSheet/bottomSheetStack.ts
index d650619165830..ca4b06f1779c0 100644
--- a/packages/core/src/BottomSheet/bottomSheetStack.ts
+++ b/packages/core/src/BottomSheet/bottomSheetStack.ts
@@ -1453,6 +1453,28 @@ function finishReplace(replaced: Entry): void {
   replaced.replaceable?.finish();
 }
 
+/**
+ * The viewport top a panel rests at: its box without the translation it is
+ * still travelling under (an entering panel rises from below the viewport).
+ * Read from the panel itself, never from the element around it: a standalone
+ * sheet's panel sits directly in its dialog, which spans the viewport, so a
+ * parent's top is not where the panel rests.
+ */
+function restingTopOfPanel(panel: HTMLElement): number {
+  const top = panel.getBoundingClientRect().top;
+  const view = panel.ownerDocument.defaultView;
+  if (view == null || typeof view.DOMMatrixReadOnly !== 'function') {
+    return top;
+  }
+  const {transform} = view.getComputedStyle(panel);
+  if (transform === '' || transform === 'none') {
+    return top;
+  }
+  // A sheet panel only ever translates on the block axis (entrance, drag,
+  // alignment); its computed matrix's `m42` is that translation.
+  return top - new view.DOMMatrixReadOnly(transform).m42;
+}
+
 function alignmentOffsetForPanels(
   enteringPanel: HTMLElement | null,
   retainedPanel: HTMLElement | null,
@@ -1460,12 +1482,13 @@ function alignmentOffsetForPanels(
   if (enteringPanel == null || retainedPanel == null) {
     return 0;
   }
-  // The positioner is where the entering sheet will rest; the panel itself
-  // is still rising from below the viewport.
-  const enteringTop =
-    enteringPanel.parentElement?.getBoundingClientRect().top ??
-    enteringPanel.getBoundingClientRect().top;
-  return Math.max(0, enteringTop - retainedPanel.getBoundingClientRect().top);
+  // The retained panel is at rest; the entering panel is measured where its
+  // entrance will leave it.
+  return Math.max(
+    0,
+    restingTopOfPanel(enteringPanel) -
+      retainedPanel.getBoundingClientRect().top,
+  );
 }
 
 /**