I practice ancient fencing.
You will never, ever, nullify protection from a shield larger than a target shield with a feint, because you simply don't move these monsters, you just use them as an "interdiction zone" where the enemy can't attack (and he indeed can ot) and sometimes you slam or bash your foe with it, if he is stupid enough to close in.
A target shield is different, it moves to protect the weapon hand or to intercept a strike while the other hand attacks (usually in the same movement). Feinting against a target shield may be efficient, but since the weapon covers the attack angles that the shield leaves open, i'd say you may lose only half the BD.
Besides this, you got it right but this method seems a bit sluggish. Maybe I'll try it.
(I am still not convinced that feint is a separate skill, it comes naturally when you gain proficiency with a weapon. As far as I am concerned, it is part of the OB)