Yes, back angle depends on anthropometry. It also depends on distance from the bar. If the bar was over your toes, you could squat to it, but your lift would suffer. I know a lifter who shifts some fearsome weights whose dimensions are such that his back is horizontal at the start.
Your set up doesn't follow the exact SS model. It would probably help you.
Put feet under bar, you do that
Bend down, keeping the legs straight, you don't do that. I've found that going from flexed back to extended helps me feel the extension more than trying to extend from the outset.
I think you could set your back in extension more.
Stance might be wider than you need, maybe.
I'm not sure that staying tight between reps is necessary. Just complete the rep, set up again and go