Tried cutting off depth a little today, to see how it impacted knee movement. This set had the "cut-off" depth (first two reps) and then my "normal" depth (last three).
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Knees still slide, but I
almost don't care, since I finally figured out how to fix the shoulder pain. Turns out I was approaching the bar wrong: when I'd initially "make contact" I'd let my back muscles be loose, so I could then tense them to "grip" the bar. Today I tried approaching the bar already flexed, creating the right "shelf" and 95% of the pain was gone.