Why dose cover not work

It's getting really annoying when your laying down behind a rock and you get killed through the rock or most times when covered. You think your safe for a moment then suddenly your dead and the kill shot shows that the person was on the other side of the cover in a place where they shouldn't be able to shoot you and they are either 10 meteres away or 200 meters awaygetting one shot kills, if I was behind a house wall I'd understand getting maybe a single hit on me if the person had the penetration ammo on but being killed out right like I was just standing out in the open is starting to make me not want to have this game anymore, aswell as other reasons for not wanting to play the game like, hit register and the inconsistant damage and explosive radius of rpgs. 

Edit: Removed profanity. Per the EA Forums rules, make sure your messages do not circumvent the profanity filter. -CM