(the last one in the last line but one, posted by phil).
I can only presume the EH engineers have calculated that friction will keep it in place.
So far as the other movement is concerned, have you been able to replicate any of the early pictures on TMA in order to show a change?
Anyway, that apart, we could have got a couple of spades out and dug down the side of one of the ends without putting the stone at risk at all of falling and told them how deep it was. We could have made a few bob out of that while saving them a few grand as well :-)
Mind you it would have taken us an age with the RL just over the road!!
I mentioned the Cove stone in the context of desk based assessments using photographs, my point being that things are not as they may seem particularly if you come it from the restoration angle (no pun intended - honest!).
I have to say looking down in that hole and seeing how big that stone actually revealed itself to be was awsome. That was some feat to get that upright. If I were there and it had slipped in I wouldn't be giving a toss what angle it was at as I would be pooped along with everyone else.