Cool, thanks for looking at it.
Another issue we have using the empty tube space instead of the “Screen Black Edge” is corner radius. The black edge it had it’s own corner radius parameter so we could match the bezel radius.
The global radius is also tied to this I think. Now the parameter doesn’t seem to have an effect, so I couldn’t use the black edge if I chose to. 
V1 release.
Newest release.
BTW Everyone. This is a WIP on the BBC Master.
This was incredibly difficult, I worked on it for most of four days.
One of the reasons it was so hard was I insisted on using my BBC Micro source, since the keyboard layout was virtually identical. (Except for the num-pad.)
It is one of the most detail graphics yet. Here is a full view.
I like it. 
It may not survive a serious OCD pass, some pieces are a little hacky and I may not be able to live with them the way they are. 