A:Answer I would say you need a rounded case. I purchased 2 of these,one for a iPhone 12 pro max that has a square edge case and it really has trouble staying on. (ESR Sidekick Hybrid Case)
I also purchased the second one for a samsung galaxy s20 ultra. It had a edge case(just covers the edges, RhinoShield Ultra Protective Bumper Case ) and it is rounded. It fits perfectly.
This is my experience and opinion. I hope it helped you