Something of a basic question here: For halftime adjustments for defensive positioning, what determines whether your defense is adjusted to the "plus" side? Is it strictly 3-pointers made by the opposition? Or is it points scored outside of the paint? Or something else? 

The reason I ask is because I played a +3 defense in a recent game, set to adjust at halftime. My opponent scored 28 points in the 1st half, of which only 4 of those points were scored in the paint (they were 3-for-8 from 3-point range). Considering the complete lack of an inside game in the 1st half, I would have expected to get bumped up to a +4 or +5 defense in the 2nd half. Instead, I stayed at +3.

I have noticed a similar result in other games as well. Am I right to conclude that halftime adjustments in the "plus" direction are based primarily on 3-point shooting, as opposed to a more general lack of points scored in the paint?