Red Dot, green dot, not dot, scope, irons or what ever,
The ideal of cover in the first place is to reduce exposure.
Learn to shoot left handed, learn to close your right eye and use your left eye when shooting the left side of a barricade.
Also when using a pistol/revolver use one hand. Again you'll expose less of your body.
Try it, stand infront of a barricade and have your shooting partner point his finger at your. Have him do it with one hand, and then two hands. See how much of your partner you can see.
Another trick. Have done it with a rifle but with a pistol using laser sights.
When I was in LE I did a lot of building searches. I carried a little mechanic's expection mirror for peeking around corners.
I've been practicing sticking the gun and mirror around the target and using the mirror to see the laser sight on the target. With practice you can get pretty good without exposing your head.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071