Hi, Gordon,
One thing that helps me (in all registers) is to go more for resonance than volume. You can't force the volume, but you can listen for your tone to "open up" and resonate more. Even if you can't blow away the 'bones, your tone will blend better and augment the whole texture of the emsemble. The Thompson book is great for developing this concept. Also, lay off the haggis!
Cheers,
Chas
Editions Bim and The Brass Press, International Music Publishing