Shorter flange distances do mean that retrofocusing design can be avoided, and an equivalent optical setup can be made much smaller. For example, a Voigtlander

Shorter flange distances do mean that retrofocusing design can be avoided, and an equivalent optical setup can be made much smaller. For example, a Voigtlander 35/1.2 lens for mirrorless full frame is about 60mm (diameter) x 60mm (length) while I don't know of any equivalent lens for an SLR that is less than 90x120mm. Also, you can't have the rear element go too far behind the flange distance of an SLR without getting smacked by the mirror. With mirrorless this isn't an issue. But you don't want your ray angles to be too extreme or the microlenses won't focus well onto the photosite.