Because I am not a pro but a reasonably intelligent and successful self-taught -- I will PM you what I suggest you do for the low register, which has worked gangbusters for me once I figured it out (and it works on all brass for me; it's just that with a horn-sized cup, it is far less obvious what ...

Thank you all for your input. As mentioned: getting the lips to vibrate with the proper aperture size for the instrument is somewhat important for proper sound production. Coming from French horn (and also cornet and tenor horn in my brass band past), learning to relax a few of those muscles that ...

One variant I've used in the past, which I quite liked, did not use the strap rings at all:

https://blaasmomusikk.no/produkter/unica-bandolaer-kryss-spesial-til-tuba-euphonium-baryton/

There's an adjustable part of it that you tighten around the bottom bow. This part has its own strap ring ...

So I have been asked to fill in on tuba in a youth band, and up to now I've been playing an old B&H Regent Eb equipped with a Kosikup mouthpiece of similar vintage. A tuba this tiny leaves something to be desired in terms of fullness of sound, so to improve on this I found a really nice Wessex ...