Yes it overlaps but in fact the wacom board is designed to be suspended a few mm above the base and what's great is it is enough for the Teensy to sit at the bottom without touching anything.
Yes on the last picture that ugly eliptical hole is the reset hole I drilled. It's not circular because I made a little mistake.
Now I've had a play the only thing that is not quite right is the pressure sensing which is erratic. eg. It jumps around (jitters) as I press harder and if I push too hard I will read a light pressure as though there's some wrap-around happening.
Tweaking the setting in the driver can make it a bit better but it's not too good. Do you have any suggestions ?