diff --git a/OpenNest.Core/Geometry/Shape.cs b/OpenNest.Core/Geometry/Shape.cs
index a2d9792..ab32d66 100644
--- a/OpenNest.Core/Geometry/Shape.cs
+++ b/OpenNest.Core/Geometry/Shape.cs
@@ -298,6 +298,7 @@ namespace OpenNest.Geometry
 
             polygon.Close();
             polygon.Cleanup();
+            polygon.UpdateBounds();
 
             return polygon;
         }
@@ -341,6 +342,7 @@ namespace OpenNest.Geometry
 
             polygon.Close();
             polygon.Cleanup();
+            polygon.UpdateBounds();
 
             return polygon;
         }
diff --git a/OpenNest.Core/Part.cs b/OpenNest.Core/Part.cs
index 312c83c..d4df8d8 100644
--- a/OpenNest.Core/Part.cs
+++ b/OpenNest.Core/Part.cs
@@ -20,6 +20,13 @@ namespace OpenNest
 
     public class Part : IPart, IBoundable
     {
+        /// <summary>
+        /// Chord tolerance used to polygonize arcs/circles for overlap testing in
+        /// <see cref="Intersects"/>. Matches the tolerance used elsewhere for
+        /// geometry-sensitive checks (e.g. <see cref="PartGeometry"/>).
+        /// </summary>
+        private const double IntersectsChordTolerance = 0.001;
+
         private Vector location;
         private bool ownsProgram;
         private double preLeadInRotation;
@@ -247,8 +254,8 @@ namespace OpenNest
             if (perimeter1 == null || perimeter2 == null)
                 return false;
 
-            var polygon1 = perimeter1.ToPolygon();
-            var polygon2 = perimeter2.ToPolygon();
+            var polygon1 = perimeter1.ToPolygonWithTolerance(IntersectsChordTolerance);
+            var polygon2 = perimeter2.ToPolygonWithTolerance(IntersectsChordTolerance);
 
             if (polygon1 == null || polygon2 == null)
                 return false;
diff --git a/OpenNest.Engine/BestFit/PairEvaluator.cs b/OpenNest.Engine/BestFit/PairEvaluator.cs
index 0e6b899..c54ec5e 100644
--- a/OpenNest.Engine/BestFit/PairEvaluator.cs
+++ b/OpenNest.Engine/BestFit/PairEvaluator.cs
@@ -13,6 +13,15 @@ namespace OpenNest.Engine.BestFit
     {
         private const double ChordTolerance = 0.01;
 
+        /// <summary>
+        /// Tighter chord tolerance for the overlap check only. Rounded-corner arcs
+        /// polygonized at the coarser <see cref="ChordTolerance"/> can "cut the corner"
+        /// enough to hide a genuine but tiny sliver overlap between two candidates —
+        /// this needs to match the precision Part.Intersects uses elsewhere so BestFit's
+        /// Keep decision agrees with the same overlap check callers rely on downstream.
+        /// </summary>
+        private const double OverlapChordTolerance = 0.001;
+
         public List<BestFitResult> EvaluateAll(List<PairCandidate> candidates)
         {
             if (candidates.Count == 0)
@@ -49,10 +58,18 @@ namespace OpenNest.Engine.BestFit
             part2.Location = candidate.Part2Offset;
             part2.UpdateBounds();
 
-            // Overlap check — perimeter vs perimeter
+            // Overlap check — perimeter vs perimeter. Uses Collision.HasOverlap (full polygon
+            // clip) rather than Shape.Intersects (edge-crossing only), which misses containment-
+            // style overlaps where one perimeter's boundary never crosses the other's.
             var shape1 = GetPerimeterShape(part1);
             var shape2 = GetPerimeterShape(part2);
-            var overlaps = shape1 != null && shape2 != null && shape1.Intersects(shape2, out _);
+            var overlaps =
+                shape1 != null
+                && shape2 != null
+                && Collision.HasOverlap(
+                    shape1.ToPolygonWithTolerance(OverlapChordTolerance),
+                    shape2.ToPolygonWithTolerance(OverlapChordTolerance)
+                );
 
             // Convex hull vertices from perimeter polygons only
             var allPoints = GetPartVertices(part1);