>>6539565It's good form so long as you keep your shoulders pinned down and your butt is still touching the bench, with your lower back kept straight. You can get some pretty extreme arches when trying to push for a personal best. But so long as someone is spotting you, it's actually safer since it's less likely your scapula will snap. Never keep your back totally flat benching heavier loads.
It's hard to tell exactly since I can't see her leg or lower back placement, Miu might be lifting her butt too much, but seems ok.
