5.4” is too small. 6.7” is too big. 6.1” will have compromises. Where do I go?!
It's possible that the 6.1" won't have compromises. Consider that the new frame will be squared, allowing strength further out towards the edges. With that in mind, the line-up could be:
iPhone 12 Pleb or Pro: 6.1" (XS was 5.8", so stretch out to edge of square frame for another 0.3")
iPhone 12 Pro Max: 6.7" (XS Max was 6.5", so again take it to edge of square frame for extra 0.2")
iPhone SE2: 5.4" (iPhone 8 was 4.7", then take away bezels and chin/forehead for another 0.7")