johnhh - 8:11 pm on Jul 1, 2011 (gmt 0)

there would be no apparent commonality at all at a macro level; only at search phrase/ cluster/ semantic level

that is possible, for example we have sections where every page (100%) ranks page 1 for the targeted phrases, and some sections where only 10% of the pages rank on page 1 of the SERPS. Yet there is no difference in any factor I can see, and no it doesn't seem to be related to the number of pages in a section, nor to page design or navigation.

Still way down on traffic though !