OK, this could be utter crap, but I'm throwing it out there.
Your arch is awesome, but your head comes up off the bench and you are up on your toes. Regardless of rules etc. what that tells me is that your angle to the bench is not at it's best. Your foot drive is pushing into your back and not your arms very much, plus some force is lost in the flexibility of your foot. So your best force into the bar only comes when your butt comes up off the bench and your angle is better.
Try heels down, arching onto your neck and heels pushing right up through, driving your upper back/head into the bench, butt barely on bench at all. With your silly posterior chain strength added to the mix, that's perhaps a boost if it works.
I'm not an expert. But I do feel there's a connection between your heels driving into your neck and force going up the bar.
I am Anton Zdravko Martin!
Best meet lifts: Sq 150 Kg (330 lb), Bench 120 Kg (264), DL 160 (352) @89 Kg (197)
Best gym lifts: Sq 375, Bench 280 (pause), DL 385 @205 or less
Goals beyond my wildest dreams, 600 Kg raw total, 200/160/240
Hack away at anything which isn't essential. Do what you love, and do it often. Fazc.
Everything competes for recovery so more assistance is not always the best idea. miked96