That is awesome deadlifting and squatting, Brute! Just the poster child for pushing progression the right way. Well done.
I'm not an expert, but to piggy back on what BtB is saying, when you set up for squats, force your elbows forward and down and feel your upper back scrunch together and how that raises your chest up. Then push your ass back first as your descend, but holding your arch, chest up.
If you watch your side view, you squat powerfully, but at the bottom and you are at the bottom, you push your ass back then to get even lower and you do go even further to rock bottom which is awesome, but that motion pitches you forward and forces your silly lower back strength (i.e. 475+ deadlifting) to pull you upright. What BtB is saying is that you did not need to go any lower once you hit below parallel, esp. if it compromises your form.
Try it chest up and ass back to start, that will naturally lower you into the "bottom" position you need as your body flexibility will not let you go any further than that. No need to force it further as that will often compromise your body position. And if you keep your elbows pointed down and kind of forcing them forward, it helps keep your upper back tighter. That's my weakness btw, so if you figure out how to do that, help me out, although I suspect it's just practice with heavier and heavier weights.
Just my .02! Just throwing stuff out there that might help, if not ignore it obviously.
Awesome stuff, Brute.
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 275 (pause), DL 370 @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.