I can only speak from personal experience, but mounting it further forward on the rail does not make the sight body disappear from your view. In fact, I have found the opposite to be true.

I do shoot with both eyes open, and when I was saying FOV I was talking about the amount of real estate visible through the glass of the red dot. When I mount my red dot forward on the rail, I get this sight picture, where the blue is the sight body image created from my right eye, and green is the sight body image created by my left (and obviously not drawn to scale):



Notice that the green sight body is due to the sight being in the peripheral vision of my left eye. This blocks and distracts my vision from concentrating on the target and lining up the dot where I need it to be.

When I mount it closer to my eye, the sight picture becomes this:


Notice that in the second picture, the green sight body is almost non-existent due to the fact that my it is now almost out of range for my left eye's peripheral vision. This allows me to actually see my target and its surroundings much better, with less interference from the "ghosting" of the sight body.

Again, this is all just my experience when trying to figure out where to put my red dot. If people aren't bothered by seeing the red dot body and prefer it farther forward on the rail, then do it and I wont hold it against you. But for me, I get the clearest and best vision from having the red dot farther back for the reasons I described here.