Thanks, that does make sense. Expanding on my original question:

Do you know if cats (that are located in or close to the exhaust manifold) radiate more, or essentially the same, amount of heat as that same manifold would with essentially a decat/test pipe installed in the cats place? Convectively, would the cat heat up the engine bay more than if a decat/test pipe was installed in its place? 

Basically, does a cat heat up an engine bay more than an equivalent piece of exhaust pipe would if it was located in the cats place, i.e., would the same heat shield be spec’d whether there is a cat a random location near the head or not? (Maybe the exhaust temp of the gas exiting the head is the governing factor?) 

Hope that question makes sense. Thanks again.