I'm not understanding what your talking about, but Super-16 goes to one edge only, and Ultra-16 goes to both edges (intersprocket).
Why would having something to support the film against the pressure plate have anything to do with how wide the gate is?
a few things going on here...
Ultra16 as has been pointed out doesn't go all the way to the edges - but it would seem that it could
go further, and hence be a better option for anamorphic
Super16 doesn't go all the way to the edge either - but the graphic in the link David provided shows that it does, which is wrong, but its the internet after all (no biggy)
Finally, you have to support the film around the aperture area from buckling or distorting in the 'Z' dimension - this is achieved with a pressure plate that bears on the base side of the film, its needs something to work against which is the aperture plate which touches the emulsion, it works both as a light stopper and as the 'registration' side of the sandwich that keeps the film on the film plane, it effectively defines the film plane ... Super16 could if you wanted fall off the side of the film but youd have no edge for the pressure plate to push against on that side and your film would fall off the film plane and cause localised focus issues. No good.
You might think well ok, then remove just the area around the actual aperture, then the light will get through and the rest of the aperture plate will support the film! But the area of film that is supported by the aperture plate (and therefore also is obscured from light) is like I mentioned 'sandwiched' this has the tendency to cause scratches on the emulsion, making the area useless for acquisition ...
There is a thin thin strip of unexposed film on the side of super16 film that supports the film on the aperture plate - check it out on the RHS:
My query pertains to Ultra16 - I see now that the claw is going to scratch the film in the same way on the sprocket side, so that is the limit there but why not extend out the other side to the super16 limit - yes, making yet another
format, like 'asymmetrical ultra16 optimised for anamorphic' - yeh, youd have to move your lens mount etc... all too unworkable - but unless that horizontal number is still not as high as the super 16 dimension it's not logically unsound