wearing the guitar low is another bad habbit.
also if you got it really low you'll end up damaging your wrist over the long run on the 9-22 frets just because of the angle your wrist has to be to get those notes.
my guitar teacher was this old psychiatrist.. who taught guitar lessons on the side. she was like 60 or so and looked like an ogre (no joke) she would be such a pain in the ass about posture, hand position finger postion, and guitar to low and everything else you can think of.
in fact my left hand technique she used to keep a sharp pencil above my fingers so if i lifted my fingerst to high off the strings i'd get poked. (basically training me from the beginning to be the least amount of distance away from the string without deadening it's sound. (which is mega helpful with speed as you can imagine)
pissed me off somethin' feirce then but i can see the benefit in it now that i'm older.
as far as how far up... it's up to you... but the center point of the guitar shouldn't be any lower than about a half inch above your belly botton.