1) what criteria need to be met to class an obviously natural feature as a genuine TMA prehistoric ritualistic site? E.g Sacred Hill, rock feature etc.
2) what other examples are there out there, aside from Capel Garmon and Bryn Celli Ddu?
It's difficult to imagine that any "sacred" site wasn't situated in complete awareness of its natural surroundings, so I don't know where you draw the line, honestly. To answer your first question is therefore very difficult. Intervisibility with other sites must score highly, but is not by any means essential. I don't know why things like the Cheesewring are necessarily TMA-ish, but it does seem entirely right that they are. Perhaps it's the fact that they were simply "there" when our ancestors were deciding to build their own monuments, which would have been seen as either embellishments to, or impositions upon, nature - I guess. Struggling, sorry!