The map showing (the very precise) inner dots...
http://www.avebury-web.co.uk/the_shame.html
http://www.avebury-web.co.uk/henge6.html
The ring stone appears to be on the same 'line' as the dots.
Well on the rubric it says 'place of a stone taken away' for a dot? Some of them have even got dates haven't they. And as you say the ring stone is on the same level.