My red dot has unlimited relief. That means my eye does not have to be at a certain distance for the "scope" to take effect. Check the relief on the device, if it is unlimited, technically you could put it on the front (but why would you?)
As mentioned above, it doesn't really matter with a 1x magnification red dot.
I find that if it's mounted over the barrel, as opposed to over the receiver, I notice more of the target and the dot, and less of the scope body. This allows for more rapid target acquisition. That's why I use Scout Mounts on my M-14's, Mini-14's, and AK's.
As said before, you can place the red dot anywhere you want because of the unlimited eye relief. That said, If the red dot is close to your eye, it will appear a little larger than if it was farther down the receiver. Also, if the red dot is close to the eye the body of the red dot will block some of the side view and you may miss some action while hunting that you could see if the red dot was farther down the receiver or barrel (think Scout style).
The best thing is that you can put it where you want it.