>>4139939~38mm is what you use if you want your image to have the same FOV that your brain does. However, it will always look fisheyed because you're not accounting for the fact that you see in stereo.
It's a constant balancing act between overall FOV and 'flatness' that is mechanically impossible to perfect with only one sensor.
~60mm is where things have about the same 'flatness' as stereo human vision, which is why 50m and 85mm are the go-to for portraits, but again this makes the overall FOV too narrow.
