Very interesting video on cap sensor design.

He has a sense plate and a ground plate that are separated horizontally so the plate fields spread out.
Then he makes the ground plate much bigger than the sense plate, concentrating potential on the sense plate.

There is also this:

I am liking the lack of resistors, etc, in the second approach, the 1-wire cap sense.

I don't like bare metal touch because of static and accidents. Touch paper over metal is better but I want plastic sheet over the paper. The button labels print on the paper, the cover sheet wipes off.