There are two exploitable bosses i found, the final statues and Sekrion... For all i know there are many more, Its to do with the larger enemies firing from a certain part of there body. This causes them to locate the player and fire at it. I found that when fighting Sekrion you could hide in the ditches right against the wall and his hits won't connect. Also with the final statue bosses because they are right handed you can hide to te right rear of cover located very close to the center of the arena, He will continue to shoot at the wall whilst being vulnerable until you kill him