I can’t seem to upload an image of my current mount, but it mounts flat on the top of my dashboard on a little plastic sheet that’s permanently affixed to the dashboard.
The mount has a suction cup made of that sticky rubbery stuff. Any new mount needs to mount the same way. I’m hoping some of you have similar mounts and have some experience with what holds such a large phone well. (I have a slim case).
I have this mount from Scosche and it’s been fine with my P7 in a Spigen thin case: https://www.scosche.com/collections/new-apple-ipad-iphone-accessories/magicgrip-mount-double-pivot I have it mounted in a lower cubby in front of my shifter with the suction/sticky attached to the top inside of said cubby, and it has never fallen off or sagged.