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How much of your right hand actually makes contract with your horn (assuming a valves-in-the-front tuba, right hand on the valves)?*

Does your forearm touch the bell nearer to your elbow?
Does your wrist touch the tuba at all?
Does your arm hover over the tuba and only your fingers make contact with the valves/thumb ring?

If the last is true for you, what is your left arm and hand doing?

* - Did anyone ever make a lefty tuba...?

My left arm is actually supporting the tuba by grabbing the top bow, the bell, or one of the large branches near the top. All my right hand is doing is operating the valves. I sometimes use the thumb-ring but more often than not.... my right thumb is either resting on one of the tubes in the valve section or hooked over the 2nd slide on a rotary tuba. All the thumb-ring does is initially register my right hand to the position of the valves. My right forearm is usually resting on the lower bell stack.

I usually remove the thumb ring (feels too restricting for my taste) and let my arm float. And my left arm usually sit on top of the top bow and either pulls slides as necessary or holds on to the leadpipe.