Mart,
The rotorhub represented 50% of the drag (parasitic only - I think) on the earlier ABC. This was a serious concern.
IMHO, a secondary concern may the rotorhub generated turbulence, plus the root vorticies, due to their interactaction with the propeller (which did not exist on the earlier ABC).
Why do you believe that the 'fountain effect' is detrimental? It is probably detrimental to a tiltrotor during hover, but it could be beneficial to a helicopter in ground effect.
Dave