diff --git a/src/kiri/slicer2.js b/src/kiri/slicer2.js
index debd1568..0d094cfc 100644
--- a/src/kiri/slicer2.js
+++ b/src/kiri/slicer2.js
@@ -400,13 +400,21 @@
             }
 
             if (opt.flats && opt.off) {
+                let add = [];
+                Object.keys(this.zFlat).forEach(z => {
+                    z = parseFloat(z);
+                    add.push(z + opt.off);
+                    if (z > zmin) {
+                        add.push(z - opt.off);
+                    }
+                });
                 // add over and under all flats by 'off'
-                array.appendAll(Object.keys(this.zFlat).map(v => parseFloat(v))).sort((a,b) => {
+                array.appendAll(add).sort((a,b) => {
                     return opt.down ? b-a : a-b;
                 });
             }
 
-            return array.map(v => parseFloat(v.toFixed(2)));
+            return array.map(v => Math.abs(parseFloat(v.toFixed(2))));
         }
     }
 
diff --git a/src/mode/cam/slice.js b/src/mode/cam/slice.js
index 8eae3408..67af4914 100644
--- a/src/mode/cam/slice.js
+++ b/src/mode/cam/slice.js
@@ -175,7 +175,7 @@
             let flats = [];
             let shadow = [];
             let slices = [];
-            let indices = slicer.interval(roughDown, { down: true, min: zBottom, fit: true });
+            let indices = slicer.interval(roughDown, { down: true, min: zBottom, fit: true, boff: 0.01 });
             if (proc.camRoughFlat) {
                 let flats = Object.keys(slicer.zFlat)
                     .map(v => parseFloat(v).round(4))
@@ -206,6 +206,7 @@
                     .filter(v => v > 0 && indices.indexOf(v) < 0);
                 indices = indices.appendAll(flats).sort((a,b) => b-a);
             }
+
             // console.log('indices', ...indices, {zBottom});
             slicer.slice(indices, { each: (data, index, total) => {
                 shadow = POLY.union(shadow.appendAll(data.tops), 0.01, true);
@@ -309,7 +310,7 @@
 
             let shadow = [];
             let slices = [];
-            let indices = slicer.interval(outlineDown, { down: true, min: zBottom, fit: true });
+            let indices = slicer.interval(outlineDown, { down: true, min: zBottom, fit: true, boff: 0.01 });
             // add flats to shadow
             const flats = Object.keys(slicer.zFlat)
                 .map(v => (parseFloat(v) - 0.01).round(5))