I'm not exactly sure what result you expected. What is wrong with the front and back extrusions in the screenshot?
Did you want to create a fence around a lot where the fence on the street.front side is setback some distance while the fences on all other sides remain on the edge of the lot? If so, then I would recommend a different approach. In your code, performing an offset to get the border faces and then performing a setback on those faces is probably not what you intended because the setback is trying to perform setbacks on all 16 edges (4 edges per border face x 4 faces).
I would recommend doing the setback first to get the polygon whose edges are where you want your fence to be. Then, create your fence. You can either create your fence by using offset and extrude (as you did in your code), or if you want a more complicated fence, you can use one of the fence rules from ESRI.lib.
Lot -->
setback(comp(fe) {street.front: 5}) { all= Lawn | remainder= FencePolygon }
FencePolygon -->
offset(-fence_width)
comp(f) { inside= Lawn | border= extrude(fence_height) Fence. }
Fence rules in ESRI.lib:
Fence_On_Polygon.cga and Fence_On_Polygon_Simple.cga create fences along polygon edges. To use these, change the code as follows:
import Fence_On_Polygon:"/ESRI.lib/rules/Fences/Fence_On_Polygon.cga"
FencePolygon -->
Fence_On_Polygon.Generate