And, the question was answered. I said geometry, which is the shaft height for a given combination, which varies. But, if you need an example of what 30% is, here you go.
If the shaft needs to be .300" below the perpendicular plane, and it is .400" below, then it is .100" more than .300", so it is 30% in error (technically 33.333333~%).
Now, if the shaft should only be .250" below the perpendicular line, and it was .400" below, then it would be in error 40%. I've had shafts as much as .380" lower than they were supposed to be. How much error is that when the shaft is only supposed to be down .300"? How about 127%. Is that bad?