Whilst i can only guess at the tubular exit i think the extention of the anvil right down is possibly aimed at increasing conditioned air flow over the beam wing. As in all reality the RB5's beam wing is one of its key features (we all know how it works in with rear susp etc...)
Perhaps the winds that can sweep through Beckets could be harnessed better at the rear end with this bigger fin.
Anyone else got any ideas?
Also i am pretty apprehensive about the new nose, i really really like the way it looks now, but if its faster then im not too fussed.