The Sony E 16-35/F2.8 GM is also designed for a short sensor-rear element distance. and "only" 3.5 stops of vignetting in extreme corners. Uncorrected.. so..It's pretty well inevitable with a short sensor-rear element distance that you will get heavy vignetting. The light from, for example, the extreme right of the rear element strikes the extreme left of the sensor at a very sharp angle. So you have to correct for it either electronically or physically. A flexible concave sensor would be one answer, but I think that would be rather too esoteric. These problems don't worry me as I mainly use telephotos and these have the rear elements well inside the lens. My Sony RX10IV gives excellent images despite heavy corrections for distortion and vignetting.