The ring or the plate? If it is the plate, round it with a file or apply some cushioned tape to it.
Thumb position may also be key. Try it on the outside rather than wrapping thumb around it.
This. Remove it and knock the sharp corner off it, apply some cold blue and reassembl.
Wrong adapter? Does not look very ergonomic. You could try the thumb on the outside, i would contact manufacturer to make sure it is the right one.
Other than that how do you like the mdt stock?
You must have large hands... easiest fix - wear a glove




























