(As some of you know, I offer several other profiles in my three-piece stainless steel line of mouthpieces. Most of the others are similar to rim profiles found on other makes and models of mouthpieces, whereby people who purchase my mouthpieces will feel like they're putting on an old pair of shoes.)
This profile itself (which I stumbled across, me being not particularly clever, and one who stumbles quite a bit) isn't much wider than the width of a typical trombone mouthpiece rim profile. (Why would it need to be?)
I do not believe that wide tuba mouthpiece rims "cushion".
Rather, (I believe) they restrict.
Rims with sharp inner edges (that are also the highest point of the rim and contact the embouchure "suddenly") do not (at least, don't in my opinion) "define". Rather, they tend to pin down the edges of the "double reed" - ie. the player's lips (as if putting paperclips on the two edges of a bassoon reed, whereby the bassoon reed would probably still vibrate, but not quite as readily nor quite as well), and sharply defined raised inner edges of rims (I tend to believe) make it very difficult for a tuba mouthpiece to float on the players face - as a tuba mouthpiece certainly needs to, considering that our lowest pitches at their loudest (assuming we are producing full, pleasing, marketable sounds) involve our front teeth being spread apart over a fourth of an inch, and our highest pitches involve having our teeth closed nearly as much as a typical trumpet embouchure.
Notice the subtle white (appears white in the picture) reflective thin line roughly a fourth of the way from the innermost part of the top of this narrow rim profile (seen below). That's the only place (or at least it's the first, and hopefully the only place, if I'm not mashing) that it touches my face. Further, even though the rim is noticeably narrow compared to most, it is also asymmetrical, whereby the outside edge falls away from the player's face.
(Maybe I should be quiet about this "secret formula"
, but anyone can copy anyone else's anything... And I'm probably going to convince about .001% of anyone reading this that it's a superior rim design. ("I won blah-blah with my blah-blah, which proves that it's blah-blah." etc.) Also (and it's not news to me 
) bloke is dumb, so this rim design has to be dumb, too. I only use this profile, but I currently use in three different donut sizes - whereby more or less of my lips are allowed to vibrate, depending on the instrument and the cup shape past the rim.
The three donut sizes that I personally use involve these three inner opening sizes:
33.2mm (candidly, not too often, these days)
32.9mm (most of the time)
32.3mm (special applications)
Ever since I began using this rim profile, I stopped being aware of the mouthpiece. I don't like mouthpieces to cause me to be aware of them, just as I don't like my instruments to cause me to be aware of them.
I realize there are strongly repeated (over many decades) theories about rims cushioning the face and high inner edges defining the embouchure...but I suspect that those theories were formulated by people who never encountered a rim quite like this one that I designed (and - just like so many things - not even with the intention of accomplishing the goals that were achieved).
I could talk about other aspects of this mouthpiece, but I've trolled quite enough for one night, and I need to go pee.
). That said, my personal practice time is quite limited - either due to the amount of work that I'm expected to produce otherwise or (having reached the front end of old age) end of day exhaustion... but I'm still expected/required by those who hire me to play to a certain standard, whereby my equipment needs to be designed in such a way that - even without having played for a week, a month, or even a couple of months - I can deliver a performance product up to a certain standard whereby those who hire me will think positively rather than negatively.