Ideal NA motor, for our heads is a DIRECT flat top, no dish, for perfect burn travel, with .022" piston to head clearence with ofcourse a P or M series head.
For Turbo motors, you NEED to ONLY have the dish as a MIRROR of the combustion chambers. I build the motors, bore, etc. then I stick EACH piston up to a P series head that has prussion blue on it, and bump each piston to the head while assembled with NO head gasket. This then gives the exact outline of the chamber, and I then cut INSIDE that area, to make sure there are no trapped areas (such as a stock dish piston on a P90 head). I ordered my last set of pistons to be 9/16" thick domes, with a direct flat top so I can machine the correct dish to get my 8.25-1 compresson ratio, and reveresed imaged the chamber on EACH piston independently and cut accordingly. I then go on the inside and lighten up the uncut areas to .200" thick. NO chamber is the same, this is a casting, thats why each piston needs to be fitted to each chamber.