Hmm... I didn't know Harry was taller in DH (because I never read all of it, I guess). I always draw Harry a little shorter for the same reason gaycrow mentioned. Ten very important years of his life where he's probably not getting the nourishment and nutrition his body needs would slighten his stature forever in my mind. Though I don't like making him much shorter than Snape unless Harry's under 17. :)