This is just the engineer in me coming out, but that flex duct that you have coming out of your reflector shouldn't be at that severe of an angle. You're probably losing a lot of your air flow with a 90 degree angle. What's happening right now is your duct fan is trying to pull that hot air out of the reflector, and it's only getting a very small portion of it due to the severe angle. Kind of like putting a kink in a garden hose- you lose a great deal of your flow. Do a 45 degree angle at most & try to minimize the amount of bends in the ductwork. Just had to do this with a grocery store I remodeled with a fireplace. Had to put a few duct fans in the fireplace venting because of all the 45s to get it out from under a mezzanine above. Looks like you're on the right track!