Now then. You've come across a very interesting point. If you want to save the archaeology at Ladybridge Farm then why harp on about the henges? Surely it should be a 'Save Ladybridge Farm' campaign! Doing a save the henges campaign just gives Tarmac room to say "We ain't anywhere near the henges!"
I know you are campaigning to save the whole area, but a lot of the time it doesn't read that way. I also know that the relationship to the henges is very important, but they are safe and people will see them as the main concern.
Anyway, back to your point. What is Ladybridge's setting? Can it have one if it's part of the setting for something bigger? i.e. would it be there if it wasn't for the henges? One is most likely the cause of the other's presence. Again, saving the key site is the most important, which as you rightly say could actually be the pit alignments, not the henges or anything else. The setting of any site that is there purely because of an earlier site is 'the other site' and nothing more. Then the original site's setting comes in to play.
Great care must be taken to stress how important all the sites are as a whole. That's why I like the sound of <i>Archaeological Complex</i> - it sounds ... well erm ... complex! And therefore important :-)