Canted Lens

The cant in the lens is by design. The front lens on all Aimpoint sights have a slight cant to them. Think of the front lens as a mirror, and the LED as a flashlight. If you have one in one hand and the other in the other, you will need to put a very specific angle on the mirror to reflect the light from the flashlight straight back to your eye. 
If the lens was flush the reflection from the LED would be directed up into the wall of the tube, and you wouldn’t see a dot at all.