I just looked at the OS map for this site and realised I actually tried to find it a couple of years ago. The problem I had was that I couldn't park easily at the base of the hill in the forest.
Assuming I can manage that this time around, is it best to approach up the public footpath to the east or the farm track to the west? I seem to remember that I couldn't see the latter last time. Have you been to the tomb & boulder burials about 7km south of the circle?