It may be better for you to hide behind something not breakable. There are a lot of environmental hazards available in this game but usually they are better to use on the enemy. If you use the stealth you will see a red cone effect that shows the enemy sight range. You can hide anywhere outside that, but during combat you have to use the Hide bonus action for it to work. The AI is really stupid, enemies will not look for you, instead they will stay put. If you still have issues targeting then just aim for centre mass, pretty sure headshots or limb targeting don't make any difference here. Also get to higher ground whenever possible.
