combustion chamber question

Race builders will tell you your looking to just kiss the head with the piston at peak rpm. I think that's nuts...lol.
That being said, a modern forged piston, steel rods, a bore of 4.03, and a redline of 6500 I would run it at .030. Bearing in mind everything has to be right. Crank needs to be checked for stroke and indexing, block must be properly line honed and square decked, rod lengths checked, etc. "Tight" means extra care by machinist and assembled. The further apart the piston and head are, the less effective quench gets.