Please Help! Letus AnamorphX on a 5D Mark III

I've got a Letus AnamorphX 1.3x on a 5D Mark III. With a 50 and 85 lens I'm fine with no vignetting. But to go wider I've got a 35mm and there's about 2mm of vignetting. I know I can crop in Davinci, which I'd prefer to use, but I can't seem to get the ratio right while trying to stick with the AnamorphX natural squeeze.

I've also looked into other lenses but there aren't any primes that really fit between a 35-50mm. I also purchased a 28-135mm zoom lens, but it had a 72mm opening, making it far too large for the Anamorphx and cropped up to about 92mm. I've been searching for another zoom lens with a smaller opening and can't find one that doesn't break the bank. So, back to looking at cropping, which I'm happy to do. I just don't know exactly how to make it work.

Lastly, I should note I am running ML on my 5D, so if there's any way to set a custom crop on that, I'm all ears.

Any and all help is greatly appreciated. I'm probably not thinking this through correctly and the obvious answer is just not coming to me. Thanks!