I'm studying this myself at the moment, so thought I'd make a observation:
In addition to SW's comments about P-factor increasing Vmca with decreasing flap, also consider assymetric lift.
More flap will mean greater disparity in lift between dead engine side (low speed airflow) and live engine side (high speed airflow due slipstream). So presumably, at higher flap settings the aircraft will be more inclined to roll, giving a higher min control speed.
However full flap would cause significantly more drag on the live engine side, tending to assist the rudder in reducing yawing moment. So I'm not sure about your claim that any change in flap from 10° increases Vmca.
cheers,
O8