So, it seems Chewy is right. After lots of testing I think I have found that the bar was a bit too low. Now I am putting it more on top of the rear delts instead of across them, with traps bunched up between my neck and the bar. Feels more on my back and is easier to get my hands into position, but still a bit wide with ring fingers at the rings, elbows can go a lot more back too. The only other spot that doesn't seem like it will slip is all the way up on my neck, but that just doesn't feel safe at all and would rather just front squat if that is where the bar is supposed to go.
The new spot is tricky to stay upright though. Going to have to start over a lot lighter than I thought I would. Tried 135 lbs because I can generally get ~8 reps at that even when I am tired, but was lucky to get 3 today. It's a completely different lift now, but I am a lot more confident I am doing it right this time, so at least I have that. Also, it seems I can get even deeper without losing the arch in my back, so I have that to deal with as well. ~2-3 inches below parallel was deep before, now it feels like a mile at least
Anyway, things looking good and shoulders feel amazing, better than ever even