What are some good options for a jazz flugelhorn mouthpiece? I have the Yamaha Bobby Shew and a nice 3C equivalent (for wind ensemble playing), but I want something that will help my range a bit.
I love my Denis Wick 2F. It is very deep (small bore).
You may be aware that there are different bore size standards, the french standard being much smaller than the US, resulting in a more mellow sound.
I never play only the flugelhorn at a gig, so I appreciate the contrast between my trumpet and my flugelhorn. I don't want to swap instruments and have the same sound. If you are in the same situation, you might consider having contrasting instruments.
The backside is of course that such a deep mouthpiece won't help your range. But I'd argue that if you pick up your flugelhorn, it is not to play in the high register.
If you really want to have something for the high register, I can only give you standard advice: find something with a rim similar to what you have and like, but more shallow. I'd also recommend to go to a shop and try some out. Just because someone else likes a mouthpiece does not mean that you would.
Note also that a flugelhorn (the horn itself) might not be built for the register above high C, as a trumpet could. With that I mean that whatever the mouthpiece, the high register may be difficult if the horn just does not want. Hence once again, try the mouthpiece for yourself before you buy.