Where to mount an aimpoint?

In the Kodiak mount thread, it was posted that the dot should be mounted to the rear of the slide. I'm wondering what the reason for that is. I've always been fond of mounting the dots forward as it seems to slow the wiggle a bit for me. That said, I've shot out a holosun and a vortex crossfire in the last 6 months... the holosun looses position, the crossfire is a battery contact issue...

How dirty does the front lens get when mounted to the rear?

Thoughts?

Always gets dirty if you don't have a sunshades. The longer the front sunshade the better.

On the gun? 

That said, I've shot out a holosun and a vortex crossfire in the last 6 months... the holosun looses position, the crossfire is a battery contact issue...

FYI,
 I had a holosun fail when mounted on a model 52 grip mount.  When I returned it to the factory they asked me if it was mounted on a slide.  They told me the holosun is not designed for slide mounting.  They cannot take the impact from the sudden slide stop.
djw1cav

I use Aimpoint Micros without shades on some of my pistols with the objective lens right behind the ejection port (no full rail to block debris) I’ve never had any issues with the lens getting too dirty that I couldn’t shoot.