FW, I don't know if this is relevant to your musings but 4 of the Rollrights struck me as having had some scraping done to the bases of the natural depressions on their top surfaces. It may be fanciful on my part as being so knobbly most of the stones have such depressions, but these 4 seemed to me to have been slightly enhanced, and one of them had an outflow groove similar to Copt Howe which again I thought was artifice.