This is understandable. Inevitably if you put enough weight you will begin to hinge forward as the force is being applied to the top of your body acting like a lever. I would suggest not to do this however as at that point it is harder to focus on your rear delts for the movement as your mid back and legs are used more just to keep yourself upright. In this case doing less is more so lower the weight a little bit and really try to focus on just hammering the rear delts
Yeah I mean ofc you want to do enough weight so you have mechanical tension. In my experience it’s about finding a weight that’s in between so I can go intense (around 12-18 rep range) while having good form. I like doing rows sometimes for rear delts if I can’t hit them with the face pulls though.