I avoid the RER at all costs - unsavoury to say the least. Particularly on the GDN routes.
Picking up 8 -10 persons per minute is impressive and indicative of the ticket less travel going on.
From my own experience of running ticket blocks on the London suburban system , you often find a lot more than ticketless travel on these excercises, was always very handy having the BTP in easy reach.....