It's funny the things you don't notice until you learn about them. I'm reading "The TMJ Healing Plan" and it mentions that forward head posture retracts the lower jaw.

So I tested by going back and forth and I can definitely feel the change between the position of my jaw to my upper mouth. Basically as the head goes forward, the jaw does not come forward as much--if I keep it relaxed. Or I can clench it to force it to stay, in which case I'm sure something else in back is getting unnaturally stretched.

Just another reason to get that forward head back--all the time.