Hello BJR
You cannot change from an 11-10 to a 12-6 and say that this "experiment" tells us anything meaningful about diameter changes.
Your engine's running characteristics (torque curve) and how they play with the dramatic change in pitch swamp out any diameter comparison.
Many of us flew 21-11's and 12-12's on normal 60 sized pattern ships with no ill effect.

take care,
Dean P.