I was looking at Leslie Grinsell's book on Exmoor over the weekend and he lists all the stone rows, stone circles and other 'stone settings' many of which are supposedly deliberate triangles, rhomboids and suchlike, and there are chapters on the different eras - could be worth getting hold of from somewhere (this one was in the reference library unfortunately)? I'm not sure if it mentioned that place specifically with anym ore details...