I believe that cam timing, overlap/duration will change the results. Also if test is done warm or cold or wet/dry (wet=oil sprayed in cylinder)
Interesting article here:
http://en.wikipedia.org/wiki/Compression_ratio
I believe the race scrutineers have a device to check compression ratio, but it is done by volume.
But enuf said, I apologize for the reply because I am admittedly a Leak-Down Bigot. But I'm trying, in a group that meets once a week, and the meds help.