Fantastic! Thanks for putting these photos up. This featured in a recent episode of the slightly dreadful 'Secret Britain' series and annoyingly they didn't identify it, (along with The Greywethers). Now I know what it is and shall be heading there very soon. Again, thanks.
We visited yesterday, saw the Clos Teg stone in the middle of the field and its partner, Y Garreg Goch in the hedge at the far side. The stone had been covered with a thick blanket of ivy, but that had been peeled off. Here's a link to more about them https://scribblah.co.uk/2016/04/22/top-heavy/