I’m cutting boxes from rectangles of hardboard, MDF, and ply. I wanted to keep it simple to line up the blank with the no-cut zones in the UI.
I figured out that the left offset from the raised part of the crumb tray is about 16mm, and 38mm from the top. I cut rectangles of scrap to 18xN and 40xN. Now I can drop the blank in up against the scrap rectangles and be sure that when I nudge the cut lines up against the edges (where they turn grey) they will be cuttable (according to GFUI) and on the board (because the board extends 2mm beyond).
For thin stock you can remove the wood and use holddowns after registering the blank.
The beauty of this is that I am not using the camera to judge the edges so the parallax is not an issue.
Incidentally, the right and bottom are about 8mm but I haven’t tested carefully.
Action shot: 18mm board to left, 40mm to top.