Cooling a T5?

Howdy everyone, hope you are all having an excellent Saturday. I have a scenario I'd like to run by everyone and see if I cant get some input for you all. I have an 8 bulb t5 I am using for veg in my closet. In my main room I have a 4x5 flower box that is running a 600 watt hps. I am sucking in air from outside the tent near the floor and am running the exhaust into my closet to help cool my veg room. It def helps keep the room cooler, however I would like to drop the room a few more degrees. My question is which will cool the lights down more? Blowing the air over the top of the fixture, or blowing the air over the lights? By top of the fixture I mean just resting the ducting on the fixture. Thanks in advance for your input!

I find that my T5 unit tends to trap the heat underneath the unit. The heat above it will naturally dissipate, but the stuff underneath seems to get caught up in the reflectors. I'd blow air across the bulbs if at all possible.