as long as both eyes are open, you wont see the scope housing. It doesnt matter if you are in motion or absolutely still. when the gun is down at hip view, it would be solid opaque. The scope is only transparent when it is held in aiming position (directly in your line of sight). Its an equal trade off of pro and con that doesnt need to be tweaked for video game 'balancing' sake. on the one hand you have a disorienting effect with the magnified image moving faster than the background, but on the other hand, the housing should be transparent and you have full peripheral awareness. In real life the ACOG is already balanced by nature. Its another unnecessary BS artificial 'game balancing' technique devs use. that way the speed of the the image moving in the scope matches the speed of the passing background image. In all games that have an ACOG, the entire screen will zoom the amount of magnification (usually 4x), rather than only what is inside the scope.
If it were modeled realistically it might actually make you a bit dizzy because in actuality with a magnified scope, the center magnified image would move 'faster' than the surrounding background.
I think the reason why everyone makes it with tunneling effect is so that you can run and move around quickly while scoped.