From past experience with HVAC systems, a jet of air from the output of a fan or duct can be directed and will "penetrate" into nooks and crannies such as between fins. The input or vacuum side will however draw very much from the zones of least resistance and at a very short distance from the inlet the air velocity will be next to nothing. The factory cooling kit may well be very deliberately arranged to blow forward to get air flow in between the fins where there is otherwise very little when stationary.
Of course, my one is on over 13K miles and is yet to go into skip fire mode without the cooling kit.
