Just received the tech support reply from Aimshot....

I asked the question for both rifles and handguns, should the sight be mounted close to the rear of a handgun, or near mid-barrel, and should the sight be mounted near the front or rear of the receiver for a rifle like an AR-15.

"On an AR15, I would recommend placing the sight over the receiver if you have a flat top. You can put the sight further forward but I find it to be more difficult to use.
On a pistol, you really dont have too many options so I would say mount it the same way you would mount a regular scope.
At the end of the day, It all boils down to what is comfortable for you. You really wont see too much of a difference in accuracy."

Not much help for my question, but it seems that it's pretty adaptable for shooter's comfort, so the "eye relief" wouldn't necessarily matter as much.

I took my Ruger out yesterday with the sight mounted towards the rear. It's definitely an adjustment to tube style optics, but I like it so far. I'm pretty strongly considering picking up another one for one of my AR-15's, and one for my fiancee's turkey gun. Definitely not as restricting as tube style scopes, but certainly advantageous to iron sights. Not sure why I waited so long to try them out!