Your call, and I'm sure you will get a slew of opinions here, but the closer it is mounted to the eye, the fuzzier it will be. i.e., the farther away from the eye, in general, the clearer it will be.

Remember tho, that the farther away it is, the closer to the front sight which means the shorter the sight radius. In general, a short sight radius is more difficult to shoot well than a long sight radius. The GUN, technically, is no less accurate, but it is more difficult to shoot accurately if it has a very short sight radius.

Might add that if you are having a sight fitted, you can play around with it before fitting, taping it to the barrel at various places and sighting it whereupon you can make a judgment of your own based on your own eyes at least as far as sight picture is concerned, if not accuracy {without shooting}.