diff --git a/src/kiri/core/widget.js b/src/kiri/core/widget.js
index 7cba6cb5..c7385295 100644
--- a/src/kiri/core/widget.js
+++ b/src/kiri/core/widget.js
@@ -913,6 +913,8 @@ class Widget {
             if (a.z < z && b.z < z && c.z < z) {
                 // skip faces under threshold
                 continue;
+            } else if (a.z === z && a.z === b.z && a.z === c.z) {
+                // skip faces coplanar with z (shadow looks up)
             } else if (a.z >= z && b.z >= z && c.z >= z) {
                 found.push([a, b, c]);
             } else {
diff --git a/src/kiri/mode/cam/op-area.js b/src/kiri/mode/cam/op-area.js
index e078b5be..5820cdef 100644
--- a/src/kiri/mode/cam/op-area.js
+++ b/src/kiri/mode/cam/op-area.js
@@ -17,7 +17,7 @@ const clib = self.ClipperLib;
 const ctyp = clib.ClipType;
 const ptyp = clib.PolyType;
 const cfil = clib.PolyFillType;
-const ts_off = 0.1;
+const ts_off = 0.01;
 
 class OpArea extends CamOp {
     constructor(state, op) {