This is probably already a well-known observation, though when performing any over presses (DB/BB)the tendancy to allow the lower back to curve away from the back of a seat is something I’m working to discplining myself against. Our gym doesn’t have ‘seats’, but rather benches that flip up, without footrests.I find when I’m lifting heavier weights or approaching potential failure, my lower back tends to bow away from the back support bench which has the potential for injury, as the weight or pressure should bare directly in line with the spine.I found with using the low-cut seats, that although my lower back was neatly pressed into the back of the seat with the foot rests, I tended to lean backwards taking the direct pressure off the delts. Just an observation I’ve experienced over recent times.
Try doing your overhead presses standing for a while. It’ll help.
I agree with zev, it’s easier to keep your back staight if your standing.
Ditto, I think you should stand. Tighten up your mid section like you would when you squat. Keep your abs tight. That should help.