360 challenge rear undertray

posted up on another forum but didnt get anything technical in response. hopefully ill have more luck here.

i was under a few challenge cars at the weekend while running my porsche cup car and looking at their rear undertrays complete with those naca ducts got me thinking in technical terms about the challenge grill on the rear of my own 360.

id never really thought about it before but was it designed to allow air to flow in through these ducts in order to expell the hot air through the holes in the rear grill or are the naca ducts purely for localised cooling of components requiring more or specific cooling on the challenges?
is the air flow through these ducts negligable in terms of passing across the engine bay itself or do they really channel air up into the bay in decent volumes hence the need for holes in the rear grill?

im one for applying function as much as possible and the thought that i may be missing the full application by only running the rear grill and not having had the undertray changed out is now irking me.