That's created a lot of difficulty for the zombie AI for sure. I can reliably get one stuck under the ramp to the delivery truck at Joe's USA and have even seen a zombie phase underground and "jump" from the outside to the inside of a closed door at a Pass N Gas. In fact, they're phasing underground and through objects quite a lot.
Basicly, walkers shouldnt damage legs and crawlers shouldnt damage torso and head
I doubt it has much, if anything, to do with zombie types, which locational damage probably should. The change to zombie behavior seems to have caused them to "attack" the player avatar's legs far more often whether they're standing/crawling or seemingly aiming for torso and head. My avatar still wound up with a concussion on occasion because I don't think there's ever been true locational damage in all the time I've tested the game. My avatar has been concussed by dogs, which most certainly didn't jump as high as its head, for example. The problem has only worsened and become more obvious since that change to zombie behavior in my experience. If they're attacking lower "blocks" now, that just so happens to be the height of the player avatar's legs as well.