You have changed the inlet air path from one that takes outside air from the front of the car to one that sucks hot dirty air from the engine compartment, air that has been preheated by passing through the intercooler, coolant radiator and airconditioning condenser. Of course it is going to be hotter. Your heat shield will have no positive effect because the radiated heat from the engine is not a significant factor.
You need to restore a cold air feed to the inlet. I think most people take a feed from the foglight area, althought I think that's a bit low and vulnerable to water ingestion in bad weather. As long as you can get a cold air feed from in front of, or to the side of, the radiator assemblies, then you should see a difference.