@Bama1fan - I recently installed a new Ring Alarm to replace an ancient ADT wireless system. I have one door contact with only about 5mm clearance in which to mount a magnet because of a deeply recessed door frame, so the standard magnet is way way too big.
I noticed that on their site Ring sells a “slim magnet” for $5, so I ordered one of those, so that’s one option for you.
However in the end I installed the new Ring contact sensor (main part, with the electronics) on the door but kept my existing old magnet which was partially embedded in the door frame. Before mounting permanently I tested that the old magnet was strong enough/close enough to the recommended sensing point and could properly detect open & close conditions for that sensor. In my case, no problems using the old magnet, which is quite a strong magnet and very close to the sensor when the door is closed.