Well, I use to shoot with my nose on the charge handle with the iron sites for a consistent cheek weld.
With the scope, I can't go that far forward anymore. After toying with the different positions, I have found a consistent one.
Basically, I extend my head as far forward looking through the site, then lowering it; having the scope hit me in the middle of the forehead. I then tilt my head back up, and there you go. Sounds goofy, but it gets me a consistent weld.
I personally love it.