Looks like you go plenty deep and you're really strong IMO, but have problem with the form.
IMO, you could try to do OL type front squats instead of back squats as the primary leg excersise on every other leg workout, to help you get a more erect posture.
Look at Olympic weightlifters when they do back squats. Perfect execution.
Why? They're used to get real low, their achilles tendons are stretched out as well as their hip extensors.
Do front squats with a olympic lifting grip, go ass to calves on that excersise.
And back off the weight slightly on the squat for awhile, just focusing on nailing the form.
Just some suggestions. Also, ask JPM about his take on it, he knows this shit.
YIP
Zack