[rubber_ducky]

There is no mystery here...

The heat shield does nothing without cold air coming through the snorkel. There is just a lot of hot ambient air in the engine bay. The heat shield is ineffective as the engine just sucks in that hot ambient air.

But, if you can force cold air into the snorkel by way of say those RPI-style scoops... then the heat shield aids in keeping the cooler air coming through the snorkel from mixing with the hot air from the rest of the engine area. And cooler air from the heat shield area is sucked in by the engine.

With the stock airbox, there is suction to suck the cold air in. Take away the airbox and the engine just sucks in hot air. So... having the intake but without the scoops, there is simply no way of bringing cooler air into the engine bay. And as a result, the heat shield may as well not even be there.

This is likely why aFe are making their own ram-air scoops.