diff --git a/frontend/src/core/components/viewer/LocalEmbedPDF.tsx b/frontend/src/core/components/viewer/LocalEmbedPDF.tsx
index 62d60e14f..f20b68b9a 100644
--- a/frontend/src/core/components/viewer/LocalEmbedPDF.tsx
+++ b/frontend/src/core/components/viewer/LocalEmbedPDF.tsx
@@ -191,7 +191,6 @@ export function LocalEmbedPDF({ file, url, enableAnnotations = false, onSignatur
           height: '100%',
           width: '100%',
           position: 'relative',
-          overflow: 'hidden',
           flex: 1,
           minHeight: 0,
           minWidth: 0,
@@ -287,8 +286,6 @@ export function LocalEmbedPDF({ file, url, enableAnnotations = false, onSignatur
               minHeight: 0,
               minWidth: 0,
               contain: 'strict',
-              display: 'flex',
-              justifyContent: 'center',
             }}
           >
           <Scroller
diff --git a/frontend/src/core/components/viewer/ZoomAPIBridge.tsx b/frontend/src/core/components/viewer/ZoomAPIBridge.tsx
index 44a4c403e..e951e76ad 100644
--- a/frontend/src/core/components/viewer/ZoomAPIBridge.tsx
+++ b/frontend/src/core/components/viewer/ZoomAPIBridge.tsx
@@ -119,7 +119,7 @@ export function ZoomAPIBridge() {
     }
 
     const fitWidthZoom = zoomState.currentZoomLevel;
-    if (!fitWidthZoom || fitWidthZoom <= 0) {
+    if (!fitWidthZoom || fitWidthZoom <= 0 || fitWidthZoom === 1) {
       return;
     }
 
@@ -143,31 +143,19 @@ export function ZoomAPIBridge() {
         return;
       }
 
-      const metrics = viewport ?? {};
-      const viewportWidth =
-        metrics.clientWidth ?? metrics.width ?? window.innerWidth ?? 0;
-      const viewportHeight =
-        metrics.clientHeight ?? metrics.height ?? window.innerHeight ?? 0;
+      const viewportWidth = window.innerWidth ?? 0;
+      const viewportHeight = window.innerHeight ?? 0;
 
       if (viewportWidth <= 0 || viewportHeight <= 0) {
         return;
       }
 
-      const pageRect = await measureRenderedPageRect({
-        shouldCancel: () => cancelled,
-      });
-      if (cancelled) {
-        return;
-      }
-
       const decision = determineAutoZoom({
         viewportWidth,
         viewportHeight,
         fitWidthZoom,
         pagesPerSpread,
-        pageRect: pageRect
-          ? { width: pageRect.width, height: pageRect.height }
-          : undefined,
+        pageRect: undefined,
         metadataAspectRatio: metadataAspectRatio ?? null,
         visibilityThreshold: DEFAULT_VISIBILITY_THRESHOLD,
         fallbackZoom: DEFAULT_FALLBACK_ZOOM,
diff --git a/frontend/src/core/utils/viewerZoom.ts b/frontend/src/core/utils/viewerZoom.ts
index 1fa1fb492..80775cfbe 100644
--- a/frontend/src/core/utils/viewerZoom.ts
+++ b/frontend/src/core/utils/viewerZoom.ts
@@ -1,6 +1,6 @@
 import { useEffect, useRef } from 'react';
 
-export const DEFAULT_VISIBILITY_THRESHOLD = 80; // Require at least 80% of the page height to be visible
+export const DEFAULT_VISIBILITY_THRESHOLD = 70; // Require at least 70% of the page height to be visible
 export const DEFAULT_FALLBACK_ZOOM = 1.44; // 144% fallback when no reliable metadata is present
 
 export interface ZoomViewport {
@@ -36,47 +36,48 @@ export function determineAutoZoom({
   visibilityThreshold = DEFAULT_VISIBILITY_THRESHOLD,
   fallbackZoom = DEFAULT_FALLBACK_ZOOM,
 }: AutoZoomParams): AutoZoomDecision {
+  // Get aspect ratio from pageRect or metadata
   const rectWidth = pageRect?.width ?? 0;
   const rectHeight = pageRect?.height ?? 0;
-
   const aspectRatio: number | null =
     rectWidth > 0 ? rectHeight / rectWidth : metadataAspectRatio ?? null;
 
-  let renderedHeight: number | null = rectHeight > 0 ? rectHeight : null;
-
-  if (!renderedHeight || renderedHeight <= 0) {
-    if (aspectRatio == null || aspectRatio <= 0) {
-      return { type: 'fallback', zoom: Math.min(fitWidthZoom, fallbackZoom) };
-    }
-
-    const pageWidth = viewportWidth / (fitWidthZoom * pagesPerSpread);
-    const pageHeight = pageWidth * aspectRatio;
-    renderedHeight = pageHeight * fitWidthZoom;
+  // Need aspect ratio to proceed
+  if (!aspectRatio || aspectRatio <= 0) {
+    return { type: 'fallback', zoom: Math.min(fitWidthZoom, fallbackZoom) };
   }
 
-  if (!renderedHeight || renderedHeight <= 0) {
-    return { type: 'fitWidth' };
-  }
-
-  const isLandscape = aspectRatio !== null && aspectRatio < 1;
+  // Landscape pages need 100% visibility, portrait need 80%
+  const isLandscape = aspectRatio < 1;
   const targetVisibility = isLandscape ? 100 : visibilityThreshold;
 
-  const visiblePercent = (viewportHeight / renderedHeight) * 100;
+  // Step 1: Calculate what zoom level shows targetVisibility% (80%) of page height
+  //
+  // At fitWidth, page dimensions are:
+  //   pageHeightAtFitWidth = (viewportWidth / pagesPerSpread) * aspectRatio
+  //
+  // For 80% of page to be visible:
+  //   viewportHeight / pageHeightAtZoom = targetVisibility / 100
+  //   viewportHeight / (pageHeightAtFitWidth * zoomRatio) = targetVisibility / 100
+  //
+  // Where zoomRatio = heightBasedZoom / fitWidthZoom
+  //
+  // Solving:
+  //   heightBasedZoom = fitWidthZoom * viewportHeight / (pageHeightAtFitWidth * targetVisibility / 100)
+  //   heightBasedZoom = fitWidthZoom * (viewportHeight / pageHeightAtFitWidth) * (100 / targetVisibility)
 
-  if (visiblePercent >= targetVisibility) {
+  const pageHeightAtFitWidth = (viewportWidth / pagesPerSpread) * aspectRatio;
+  const heightBasedZoom = fitWidthZoom * (viewportHeight / pageHeightAtFitWidth) / (targetVisibility / 100);
+
+  // Step 2: Compare with fitWidth
+  // Use whichever is smaller (more zoomed out) to ensure both constraints are met
+  if (heightBasedZoom < fitWidthZoom) {
+    // Need to zoom out from fitWidth to show enough height
+    return { type: 'adjust', zoom: heightBasedZoom };
+  } else {
+    // fitWidth already shows enough
     return { type: 'fitWidth' };
   }
-
-  const allowableHeightRatio = targetVisibility / 100;
-  const zoomScale =
-    viewportHeight / (allowableHeightRatio * renderedHeight);
-  const targetZoom = Math.min(fitWidthZoom, fitWidthZoom * zoomScale);
-
-  if (Math.abs(targetZoom - fitWidthZoom) < 0.001) {
-    return { type: 'fitWidth' };
-  }
-
-  return { type: 'adjust', zoom: targetZoom };
 }
 
 export interface MeasurePageRectOptions {