I don't know... maybe I'm the oddball here, it wouldn't be the first time... but I will openly admit that smaller, more shallow pieces definitely DO add to my range and always have.
I used to use the trusty 3c for just about everything and then I discovered the common 13a4a... big range increase. Played lead type stuff on that for several years while still using essentially a 3c for "all around" Then a couple years ago I played a 6a4a and got another couple notes on top of my range immediately. Now I am playing an ACB TA Screech as my lead piece (very close in size and feel to the 6a4a) and loving it with more range and less effort than any time before (and I'm NOT practicing 3-4 hours a day like I was in college).
I've always wondered about this phenomena and how some (apparently a lot of) guys say they have the same range no matter the piece while other say the piece makes a big difference. Is it a mental thing? Is it HOW different people approach the high stuff and different techniques depend more on the equipment?
Anyway... just my thoughts and my confession that my range IS dependent (somewhat) on mouthpiece. :)