They would have to have a closer dimension from the wrist pin to the top of the piston, or a recess cast into the top. As long as the piston comes to the top of the block and the head gasket thickness is the same, the only way to lower compression pressure would be with a dish-top piston.
Jerry
Compression ratio can also be altered by adjusting the height of the top ring land. This method is not talked about often. In fact, I'm not even 100% schooled on it myself, but if my memory serves me correctly big block chryslers were one engine where you could get multiple top ring height pistons that affected compression ratio.
