I have a Russian rangefinder lens of 35mm focal length that gets quite close to the film. But the rear element is quite large, too. At that focal length, which is really only a little shorter than the 43mm format diameter, the falloff is not important. The rear lens cap is deeper than it is wide.
Very wide lenses for rangefinders still have somewhat of a retrofocus design. I've looked at the 12 and 15mm Voigtlaender lenses for the Bessa rangefinders, and they were both absolutely retrofocus designs. But they were not as extreme in that design as SLR lenses. You could tell by looking, though, that they had one or more negative meniscus demagnifiers on the front and a more normal gaussian lens behind it, like most retrofocus lenses. They probably did that so that the lens would not have to project too deeply into the box and fit through that smallish opening, past the rangefinder follower and the meter device. I haven't looked at, say, the 43mm lens for the Mamiya 7, but I'll bet it's similar. None of these are symmetrical in the way large-format wide-angle lenses usually are.
There is another point, too. If a wide-angle large-format lens has abundant coverage and is used without movements, it might not need the center filter. But it might well need it when used at the extremes of its coverage. I don't use a center filter for a 90, but I might need to if I really pushed its limits for critical work with narrow film. I absolutely use the center filter for the 65--I'm always close to the edge of its image circle. That's a problem for smaller formats only when using extremely short lenses and lenses with movements, neither of which dominate the topic.
Rick "who can attest to the three-stop dropoff at the edges of the Super Angulon coverage" Denney