BF109 - Can't we just have the gunsight in the middle?

First you won't need a big shift in the 109. And I would also say that the required shift is by far less than in the image you're pointing me to. IF distance of the light source is significant at all which I still doubt. The limiting factor is the size of the reflector glas, not the distance. The distance only plays a role because of optical size reduction with increased distance. But this factor is irrelevant for a particularly designed light image projected actively at a certain angle on the reflector surface.

EDIT: Also reflector surface sideway inclination plays a role (see last picture in my post)