The metal will absorb & retain heat, then transfer it to the intake charge side of it much worse than plastic will though!
Also the thicker the design the less transfer from one side to another. You used very thin metal plate.
Do you have a product over there like "plasti-dip" ? A 1/8" - 1/4" coating should help quell some the transfer problems since the metal is so thin. (it won't retain a lot of heat being thin - A plus!)
Did you enclose the bottom portion as well?
Heat rise from below is a big factor in heat soak (electric fans, radiator wash, transmission)
