I can honestly say that I've never had this problem!
I am so tall that I usually get our conductor complaining that my bell is pointed right at him while the rest of the section is pointed down towards the floor so he hears only me! Hey I can't help it man; I'm 6'3"!
Anyway all of Rowuk's suggestions are pretty much what I was going to chime in with so try some of those suggestions and get back to us.
Good luck,
John