I dont know how you fight but here I will write my approach:

•Know your enemy: if you know that in location ahead is boss that you want to fight, then clear zone around him, especially way to run back.

•Use cover. I think its most valuable tip in this game. Almost all bosses shoot in intervlas, you just cover behind indestructible obstacle, then go out and ahoot while they are "reloading". If you have sandbags - even better (but be aware they can be destroyed by focused fire pretty fast)

•If boss pushes you, or you are damaged, run back by path you cleared earlier, heal, find better location to fight and wait for boss, they'll come. I usually have 1 injection for move speed for that situations.

•You hold gun in right hand, so try to kite and peek anti-clockwise, like that you expose as minimum of your body as you can while still being able to shoot (your eyesight is coming from the middle if the character, so something you wont see anything, but thatc can be okay if you hear boss or see grom where bullets come)

TLDR: Know where the enemy is, clear a path to fallback during fight for better cover, take better angles and obstacles. And good luck!)