I like the idea of having a shield there.....
But in the cause of this part it's not really a shield, it's an absorber!! Since its black, it's going to covert radiant energy from the engine/DP INTO heat. For it to reflect the long wave radiation, it would need to be light colored or shiny.
When I needed to remove my heater box a few months ago, I left the shield off because I wasn't going to pull the engine to put it back on. I have been thinking about lining my heater box with shiny HVAC tape though.