Yes, they can be at an angle, I did that with one, but then changed it, did not like the way it looked . . . you might want to consider the “slim magnet” available on the Ring website for $5. It is really small and the angle will not be all that noticeable on the molding. Mount the sensor flat on the door and put the small magnet on the molding. I used a bunch of those small magnets around my house.
https://shop.ring.com/collections/accessories/products/alarm-slim-magnet