"Brian, do you think Tiger's head is too far up at address?"
Too far up for what?
"Well, his head bobs a lot on the downswing and many think this is his problem."
His "problem" is that besides swinging too far inside-out, he does 5 other things that make the ball go to the right, and he is trying to hit a draw.
"But, you said his head won't bob if he started it lower—like Nicklaus."
First of all, to me, a head "bob" is only what the head does from the perpendicular to the target perspective.
For example, with a "down the line" view, the golfer puts his head on a different angle then it was at address, fairly early in the downswing.
But, as the axis tilt occurs, IT SHOULD GO DOWN AND BACK A BIT.
"What??? Isn't it supposed to be at the top of the tripod—totally stationary."
According to a THEORY or two. But common sense and a little time looking at the great players swings, show that a point between the shoulders is the true hub of the swing.
I don't really teach head position except at address, I teach torso position during the swing.
"So, what about Tiger's head? What would you do about it"
I'd have his eyes more at the ball at address, and then I see if that made it better or worse. (Now by better I mean the BALL FLIGHT!!!!)
If it was better, we'd keep it, if it was worse, I'd go back.
"But then his head would bob."
At the end of the day, he does a great job of keeping his hub steady.