Good question, and you need all your engine's parameters by actual measurement not listed or assumed numbers.
I'm not familiar with the sealed Power pistons but they most likely have 8-16 CCs of valve reliefs, depending on the number of reliefs and depth of cut, which will drop the compression.
Static compression ratios mean little, cylinder pressure and dynamic compression are the important numbers.

I use zero deck height, that provides good quench, depending on the shape of the heads combustion chambers and provides for better fuel air mixing. The only negative I can think of with a zero deck height block is if you blow a head gasket and need to resurface the deck to correct an erosion, the pistons will have to be shaved as well, or replaced with lower height pistons.

Ask your machinist the reasons he thinks 20 in the hole is superior to zero deck, his/her answer may enlighten us all.