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

Lixma, mh. Perhaps we're talking about two slightly different things. I do understand that even if only one eye sees an image the other is made to believe that it also sees this image. This I can understand. Provided they see the SAME image.

What I find hard to believe is that according to your images the brain is capable to add stuff. In the case of the 109 it would be the other half of the circle, something the right eye would not see as it only sees the left half of the circle.
Also the Apache Hud view is strange. As depicted the brain is obviously capable to make the eye without hud see the numbers whereas the eye with the visor doesn't.