Well, to the extent the +3 (or 2 or 1) has an impact, surely a lot rides on who you send out to play that defense. In a league full of Nashes and _______s, you end up with a lot of weak perimeter defenders and enhancing their limited prowess doesn't turn out to be a difference-maker.
I think I've used the defensive settings to some effect...but maybe I believe because I NEED to believe.