Depending on the state of the engine anything around 160-180psi is quite common, look more so for even readings across all 4 rather than just compression.
Compression and comp. ratio are two different aspects so fiding a correlation between to 2 might not be possible....especially from 7.2/7.5, its not a massive void really. The cams(worn/new?) and cam timing will also have an effect on compression.