the more I think about it, it isn't the overlap that lowers compression test numbers. it is the intake closing event. that is the only open valve on the compression stroke. but there is about 60 degrees ABDC the intake is open while the piston is trying to compress the air. and the hotter the cam, the longer the valve is open, cutting into compression time.
Thanks for all the replies and especially for explaining the dynamics involved. I now see why the cam manufacturers require/specify increased compression ratios as their cams get "hotter".
