Keeping baby from slumping in car seat?

Haley

He slumps down a bit in his car seat. He can already hold his head up so I can't figure out what's wrong? Does it look safe/ok to you? The straps aren't tightened down yet in this pic but when they are he still does it. This pic is older but the issue is still there - also please disregard the hoodie folded over his head 🤦🏻‍♀️