reflecting ballast heat away

i have a small cabinet with a 150w hps lamp. the ballast is connected and i'm having too much trouble keeping the temp down.

i was thinking of installing a barrier under the ballast to compartmentalize the heat away from the grow area.
will this help?
what kind of material?
i was thinking just a sheet of metal, maybe an inch away for insulation,, but then i considered fire brick, or blanket. can i use mylar somehow?

i have the air flow optimized for my situation.

can you make the ballast remote? take a look at the link in my sig.