hmm, i just tried your suggestion and it makes the horn more top-heavy to me, though perhaps slightly better for mouthpiece position. i didn't find it uncomfortable before. it's all a balancing act anyway. i might give it a shot at my next gig though.
It can be fun to be the only tuba/Sousaphone in an excited crowd - but it is a strange feeling sometimes!
I agree with the comment about the bell position needing some change, but for a different reason - when you are playing in an ensemble either you will be facing away from the audience or your bell will. I have noticed a lot of Sousaphone players in "alt.brass" groups trying different alignments - I am not sure if it is because they never learned the basic balanced position, or if they are experimenting with non-standard positions.
In the long run, whatever works best for you is "right."