Before we get off track, I'd like to interject a way of solidifying the correct head position. It's simple and you don't need any gimmicks to get it to work.
First, I'll say that sometimes we may get our head position out of alignment because of aiming the shot using our non-dominant eye. We stand behind the shot and sight it, but our passive eye is looking at the shot. We get down and we're looking across the shot, like in the Youtube video. It's very common and creeps into most players' game as fatigue sets in or a bad PSR is used.
The simple method is to take your bridge hand as you sight the shot standing, and put it up to your nose vertically facing away from your face. The first knuckle of your index finger will be on the tip of your nose forming a wall between your eyes. Does anybody remember how Curly Howard used to stop Moe from poking him in the eyes? Like that.
As you sight the shot, you'll notice one eye is looking at the shot even though the other eye is open and looking at the object ball, too. The eye that sees the shot more predominately is your dominant eye. The placement of your cue stick won't change, it will be where you normally place it below your chin.
What you're doing is eliminating a portion of the binocular vision that your brain receives and chooses to use for its go to picture. You're forcing the brain to choose the mainly dominant picture with as blending from the other eye like you normally do. But now, the other passive eye is supplying depth projection only and not trying to interfere with the dominant eye's aiming.
If you close and open each eye, you'll see which one is supplying the aiming alignment info and which eye is not. Both eyes are open and looking at the shot as you do normally, but they are not fighting each other. The binocular vision is dampened and the brain defaults to its eye that it uses for body alignment.
If this doesn't get flamed, I've got more.
Best,
Mike