Good question: That is why there are deep valve reliefs in those types of pistons. Checking piston-to-valve clearance in a 10:1 SCR 340 with KB flat tops at .000" deck clearance, there was something like .120-.150" clearance with a 268 duration cam in at 107 degrees ICL and 1.6 rockers with valve lift at around .490"/510". It was so much clearance that I did not bother to measure it closely.
