diff --git a/src/stitching_scanner.py b/src/stitching_scanner.py
index e37f2fc..8161327 100644
--- a/src/stitching_scanner.py
+++ b/src/stitching_scanner.py
@@ -162,17 +162,17 @@ class StitchingScanner:
     def _blend_horizontal_at_y(self, base: np.ndarray, strip: np.ndarray, 
                             blend_width: int, append_right: bool,
                             y_offset: int = 0) -> np.ndarray:
-        """Blend strip horizontally at a specific Y position in the mosaic."""
         h_base, w_base = base.shape[:2]
         h_strip, w_strip = strip.shape[:2]
         
-        # Clamp y_offset to valid range
+        # Clamp y_offset
         y_offset = max(0, min(y_offset, h_base - h_strip))
         
-        # Early exit: no blending possible
-        if blend_width <= 0 or blend_width >= w_strip:
+        blend_w = min(blend_width, w_strip, w_base)
+        
+        # Early exit: no blending
+        if blend_w <= 0 or blend_w >= w_strip:
             if append_right:
-                # Create result with expanded width
                 result_width = w_base + w_strip
                 result = np.zeros((h_base, result_width, 3), dtype=np.uint8)
                 result[:, :w_base] = base
@@ -181,45 +181,50 @@ class StitchingScanner:
             else:
                 result_width = w_base + w_strip
                 result = np.zeros((h_base, result_width, 3), dtype=np.uint8)
-                result[y_offset:y_offset + h_strip, :w_strip] = strip
                 result[:, w_strip:] = base
+                result[y_offset:y_offset + h_strip, :w_strip] = strip
                 return result
         
-        blend_w = min(blend_width, w_strip, w_base)
-        
         if append_right:
             result_width = w_base + w_strip - blend_w
             result = np.zeros((h_base, result_width, 3), dtype=np.uint8)
+            
+            # Step 1: Copy entire base
             result[:, :w_base] = base
             
-            # Extract overlaps at the correct Y position
+            # Step 2: Copy non-overlap portion of strip at correct Y
+            result[y_offset:y_offset + h_strip, w_base:] = strip[:, blend_w:]
+            
+            # Step 3: Create blend
             alpha = np.linspace(1, 0, blend_w, dtype=np.float32)[np.newaxis, :, np.newaxis]
             base_overlap = base[y_offset:y_offset + h_strip, -blend_w:].astype(np.float32)
             strip_overlap = strip[:, :blend_w].astype(np.float32)
             blended = (base_overlap * alpha + strip_overlap * (1 - alpha)).astype(np.uint8)
             
-            # Place blended region and remainder at correct Y
+            # Step 4: Place blend (overwrites part of base at correct Y)
             result[y_offset:y_offset + h_strip, w_base - blend_w:w_base] = blended
-            result[y_offset:y_offset + h_strip, w_base:] = strip[:, blend_w:]
+            
             return result
-        
+            
         else:  # append_left
             result_width = w_base + w_strip - blend_w
             result = np.zeros((h_base, result_width, 3), dtype=np.uint8)
             
-            # Place strip at correct Y position
-            result[y_offset:y_offset + h_strip, :w_strip] = strip
+            # Step 1: Copy ENTIRE base shifted right
+            result[:, w_strip - blend_w:] = base
             
-            # Copy base (shifted right)
-            result[:, w_strip:] = base[:, blend_w:]
+            # Step 2: Copy non-overlap portion of strip at correct Y
+            result[y_offset:y_offset + h_strip, :w_strip - blend_w] = strip[:, :w_strip - blend_w]
             
-            # Extract overlaps at correct Y position  
+            # Step 3: Create blend
             alpha = np.linspace(0, 1, blend_w, dtype=np.float32)[np.newaxis, :, np.newaxis]
             strip_overlap = strip[:, -blend_w:].astype(np.float32)
             base_overlap = base[y_offset:y_offset + h_strip, :blend_w].astype(np.float32)
             blended = (strip_overlap * (1 - alpha) + base_overlap * alpha).astype(np.uint8)
             
+            # Step 4: Place blend at correct Y
             result[y_offset:y_offset + h_strip, w_strip - blend_w:w_strip] = blended
+            
             return result
 
     def _blend_horizontal(self, base: np.ndarray, strip: np.ndarray,