>Of course, there are so many monuments around there, it's almost too easy to get 3 in a line

There must be some way of using statistics <bleh!> to infer likelihood of alignments occurring by chance. Then as you say there's the issue of intervisibility. It wouldn't do to just go drawing lines on maps between things that could only be seen to be in alignement if the viewer were aloft. That would be a bit too Von Danikenesque, hence open to academic ridicule.

It might be an idea to cut out the BA stuff like those Windmill hill thingies, that would make any alignments seem more robust, but then there's always the possibility that any human effort at Silbaby could be later than the BA.