Richard,
Just to clarify a point, the aperture is the hole you make with your embouchure, not a mouthpiece feature.  A large mouthpiece like a Schilke 24 requires us to use a smaller aperture in order to play the same note that a larger aperture could play on a shallow mouthpiece. In other words the hole you make when you play a high C on a Schilke 24 is going to have to be much smaller than the hole or aperture you would need to play the same note on a 14a4A.  This is the reason why shallow mouthpieces make the upper register easier for most of us.  It is also the reason why someone who always plays big mouthpieces might have a little trouble adjusting to a shollow one, as they play an ascending scale, they make the aperture too small too soon, cutting off the note.  Sometimes when this happens people think they have bottomed out, but it is more likely they have simply pinched the aperture closed. This is an ESSENTIAL CONCEPT to understand if you are going to be switching mouthpieces without benifit of warming yourself up on each one before playing it.  This small aperture is the whole concept behind Cat's 20-minute g exercise at ppp.  It is also the concept behind much of Mark Van Cleave's high note discussion.  On a more philisophical note, bigger isn't necessarily better, although it might be in some cases. More is more, better is better, sometimes more is better, sometimes more is worse, you get the point.

John Daniel
Prof. of trpt
Penn State Univ.