Lone,
I have done a bit of formation flying in both helicopters (a whole lot) and airplanes (a little bit).
I very much understand why we stacked up in helicopters and not down.
In Roll Off.....my interest is the fact the strength of the disturbed air can cause an Upset of the following aircraft.....as Helicopters do not try to roll upset down when encountering the wake/rotor turbulence of the preceding aircraft.
It is the loss of Roll Control that I find so interesting to consider.
As many have said....these things are Tiltrotors and not Helicopters. (....or Airplanes either for that matter.)