Maybe cos it's nearly impossible to get anything low out of an imperial? (Although that might just be the fact mine had a dodgy player on the end of it.)

I played one for 3 years with YBS juniors, and it'd sing at the high stuff no problems cos it had such a narrow bore. But low notes? Forget it. Had to lip everything below a low G down and they were still sharp. Much prefer the wider bore of the sovereign. Much warmer, rounder tone.
Looks like I'm just gonna have to try lots of different things, stick at it and see what works. Just like learning again!