That looks like the Xbox Pelican Rifle! Thats pretty darned cool man. maybe you could turn that eye peice for the scope clockweise about 45 degrees so it would be facing the right side of the gun away from the user and when you used the scope it would kind of conform to the right side of your face/head. Just a thought. Mess around with it, and good luck!
It could be that the gun is at a funny angle and the scope appears to be farther toward the rear of the stock than it is. IF I use my imagination and tilt the gun around to a perfect strait side shot the scope moves way forward.
Noone can see the other side of the rifle anyway, it could also be that the scope assembly moves hydralicly back and forth.