"The cups with the wide rings are quite strange ..."
That, I think, seems to be one factor that separates Irish RA into two groups. There are the heavy-duty C&Rs like these and there are the slender, more English looking ones such as this
http://www.megalithomania.com/show_site.php?site_id=1216&image=3792
However, the two types do appear together as at Drumirril (above). I don't know if Shee-Twohig split Irish RA up by this difference, but I certainly think it's worth considering. Were there two RA cultures in Ireland and were places like Drumirril seen as potent to both?
Oh and here's another I'd like an opinion on from a UK perspective:
http://www.megalithomania.com/show_site.php?site_id=559