It is not a matter of weapons. Just by being in the open and seen makes you a target. The enemies follow a pattern and they only shoot at players that are visible in their radius. I have tested this with Aetheon. I am usually the only person shooting Aetheon, and yet he continues to fire at me even if i am in cover. All my teammates are hidden, but Aetheon continues to fire in my direction. He will continue to fire at me until another person comes within his radius of sight.