" An aperture sight is best when close to the eye so diffraction effects can cause you to automatically center the front sight and target."
It may well be "best" that way (a subjective term). However, that does not go to prove that it cannot work with the aperture distanced from the eye. In fact, as I said before, the eye will centre the front "sight" (or in my case, the target beyond) in the aperture automatically, regardless. The only caveat being that the aperture, placed at a distance, cannot be so small as to prevent a clear view through it. Nevertheless, I use a (front-mounted) aperture of 0.215" in diameter. I am using this system on a short-barreled Mauser carbine (17.5" barrel). My rear "U-notch" sight is ahead of the receiver, on the barrel, giving a relatively short sight radius (which, in and of itself, is not the most desirable arrangement, of course). Works very well for me, though.
The efficacy of an aperture, placed some distance from the eye, is EASY to prove. Simply create a test "rig", consisting of an aperture of some sort, placed a given distance from the eye..... and use it to sight on an aiming point, such as a (suitably sized) dot on a sheet of paper. You will see that your eye will still work to centre the dot in the aperture. Add a "rear sight", which could be a U-notch, or even another aperture....and you have a sighting system. Add adjustability for windage and elevation.... and you have a very usable sighting system. The advantage being that it gives an unrestricted view of the target (no front post to subtend the target face).
As I said, it works very well for me. Might not be someone else's cup of tea, though.....which is just fine.
