I use foldable car sun shades, the kind with the spring steel rim that fold up. In Arizona there's always 1 or 2 in the car anyway. Set small stones or clods in the corners to hold down in light wind. Silver and reflective makes it easy to see.
I'm using a Samsung S9+ in a rugged case and found the same problems occurring. After trying several 3d printed adapters, I finally just used a sharp knife and trimmed the slot in the rubber bumper a little deeper. It works now!