I am only guessing @ this, but I think the design was to catch some air from under the car and funnel it between the heat sheilds and the manifold/header to help catch some of the hot air and push it out the back. If I remember correctly I could put a finger on the heat shield for a sec also right after driving it when it still had the black coating on it.

 

the heat sheild is there so that you do not make physical contact with the header, because it is so hot.

 

Jet Hot Coat will be int only coating you can do to your headers to make a significant differenct in the underhood temps.

 

FYI: The Heatshield temps out @ 225-250 deg, the area underneath is over 500deg as it is puts my temp gun out of range. Measuring right at the flange it is between 350-400 deg.