I've not been able to get those plugins to function for many months - but

Perhaps there is a site below the mountain stone where it is in clear view on the horizon. Perhaps there is an azimuth indicated by the stone - a limb of the setting sun or moon on a specific date perhaps. Maybe it is from one of the two stone circles that are listed or maybe it's from another different site that may, or may not, be known and may, or may not, remain. It takes a fair bit of wandering about, this way and that, but it's surprising how specific these 'corridors of alignment' are. In Northumberland there are the curricks, which are the same size as your rock but built of drystone, doing the same kind of thing. They are useful as 'lost site predictors'. Allegedly !