Cam timing has no effect on compression ratio, but has a dramatic effect on cylinder pressure at a given RPM.

At 0 RPM, maximum pressure will be generated if the valves open and close exactly at TDC and BDC. Cranking speed is effectively about 0. At higher RPM, the valves must close after BDC/TDC to get maximum volumetric efficiency.

If the camshaft timing is moving around during the test, because, for example, engine oil is running out of the adjusting mechanism and back to the pan, intra-cylinder comparisons are pretty much impossible to determine.