I used to have it mounted in front of the carrying handle, but now have a flat top and a rail system as the handguard.

Now I have the option of mounting it as far front or back as I want.

It is an EOTech with the circle and red dot in the center.

I did notice that when held close to the eye the circle and do are much larger then when held further away.

Is there an optimum distance the EOTech should be mounted from the eye?

I mount mine on my FF rail on the handguard. That is pretty much where it would be if I had a carry handle mount. I recomend that you try it in a few places and pick the spot you like best.
Here is mine.

what kind of carry handle? removable? or fixed? that may dictate where you mount it, unless you invest some $$$ in a special mount...if you have a flat-top, then mounting location may depend on distance to target and target movement..it would seem mounting it closer to your eye would be helpful if the target  is close and target  moves..if your targets are 75m - 100m + and stationary, then mounting it farther away from your eye might be better..experiment with both !