Bah... the size of the diameter of the inner rim and depth of the cup will help with increasing pitch. So the smaller the diameter and shallower the cup, the higher the range. The trade off is warmth and ease of hitting lower notes.
Think of whistling. When you tighten up your mouth and decrease the amount of air in your 'whistle cavity' the higher you pitch goes. Same principal.
I can't remember which mouth piece is smaller.
This post was edited by Superchum on Oct 18 2010 03:41pm