compression vs. compression ratio

There is no accurate way to do what you are asking. the only way to "know" is to take a head off and measure some stuff. Cranking cylinder pressure is effected by the static compression ratio of the piston/gasket/chamber combination, and the closing event of the intake lobe. It is not effected by overlap, the exh has nothing to do with it. What is your exact setup..heads, block, gasket, cam, work done, etc? and what do you have for a reading now..