The background/foreground layers I'm drawing all have that little curve in the corners left over from the full frame. That gives them a common 0,1 on both x and y. The seg layer doesn't have those (or anything like them) so it doesn't have a common scale with the backgrounds. It looks like this...
[Linked Image from choccyhobnob.com]

The position of the bounding box seems pretty arbitrary so it is very difficult to take that layer and put it over my backgrounds to check them for alignment problems. Adding something to the corners (even if its opacity is set to 0%) will force the frame to match and makes lining everything up a trivial process.

Also these overlays should be slightly transparent so other layers show through. I've made them opaque as I assumed you would be setting the opacity in the driver. Would it be better if I set the opacity in the vector so the code doesn't need to do it?