This is most notable with Hagedorn, but it is not solely this boss that has this issue, he's just the clearest example I can give.

When fighting Hagedorn he has a laser-beam kind of attack that is about 0.5 meters in diameter and shoots in a straight line. When playing multiplayer, not always, but often enough, Hagedorn will do this attack and even though me and the buddy playing with me are 90 degrees apart from each other in relation to the boss' view, and are about 20 meters from that boss and each other, we both get nuked by the attack even though according to the animation, one of us is 20+ meters away from the animation.