Specifically, I can't find a built-in modifier that narrows the middle of the jaw. I am trying to find a methodical way of matching to an image and got stuck because if I horizontal scale in order to get the sides of the face in the right place, there doesn't seem to be anything else that will pull the middle of the jaw inward, everything seems to be localized at the back of the jaw and the chin. Even turning the head shape to 100% inverted triangle isn't enough to make it fit, the mid-jaw always bulges out. It's not exactly a freakish jaw so I am surprised that I have to resort to creating my own target, and especially that there aren't any built-in targets that address the mid-jaw.
Is there a target that I'm overlooking?