Man, apparently my rule of thumb for compression values is based on flawed logic. I know the method for calculating compression ratio based on volumetric measurements would point to a direct relationship between engine compression and atmospheric pressure but apparently real-world measurements don't bear this out. I guess the main thing is that the values are near what the mfr. says they should be and aren't too far apart from each other. In other words, we still have a problem with the center two cylinders here.