Compresson Question X Heads

Purchased the Kieth Black Hyper Pistons that talks about .018 out of deck. Stock Compression of 10:2:1. Everything I read on X heads shows 72c.c. At 72 c.c the compression is 9.5:1. The piston is a stock replacement. How did Mopar achive or claim 10:2:1. What am I missing ????.
At 9:5:1 how can I bump up the compression or do I have to purchase the 62 c.c Aluminum head ?:prayer: