Sorry Clive, i cant remember. Its around .200" from memory. That could have been for turbo applications tho. The minimum depends on piston material and bore size also.
A question for an engine builder..

It would certainly be the best way to drop the comp. Leave a squish band around the edge of the piston. you wouldnt have to take much off.

If you could take 2mm off the top, leaving an 8mm squish band would drop your comp ratio to 11.6:1

so you would be removing 61.5mm diam x 2mm deep material.


Edit. this is presuming pistons are flush with with the deck. You might be able to get a little bit out of the combustion chamber also.