Perhaps you are right, I'm thinking in terms of a progression - Cursus - hidden by trees, no need for a real landscape impact. This may explain why at a later stage, when the landscape was better cleared of trees the monumental henges came along - seemingly designed for external visual impact. Then in locations where tree coverage was largely gone, the unusual had an opportunity to make a significant impact without needing to be large - stone circles? I'm generalising about timescales I know, but then I'm sure the course of deforesting would not have been uniform. could this be related to the variation in stone circle chronologies and also the lack of them in some areas.