I understand how you calculated it, but the compression ratio does not change unless one of the two volumes (cylinder, combustion chamber) changes.
The answer you got doesn't tell you anything, don't bother with "dynamic compression".
The actual cranking pressure is only distant related to that calculation.
More information in my article here: http://victorylibrary.com/mopar/blower/blower-engine5.htm
Look for "Compression ratio"