I'm not sure why you're seeing that pressure discrepancy then. It should be slightly HIGHER than calculated pressure. Something is not as it seems.
Is the engine running well? If it's doing well the way it's tuned, then it may be time to start backing into the numbers to try to figure out why the pressure is wrong. Gee, that's probably the point of this post isn't it
If it isn't doing well, then the low pressure is likely the reason...root cause could indeed be a hose flapper, plugged vent, kink, etc.
Spud