I have about the same space as you have, I just haven't taken out the shelf yet.. so I have less height.
I draw air from a few feet above the lights using a hand me down slowed down 6" vortex type fan (Was 220V, is running on 110V). The lights blow heat out in every direction, so you are gonna have to tackle the closet as a whole.. I leave more gaps in my curtains (I use dark blackout style curtains with a white lining that are slightly breathable but don't let light in) around the bottom and have a small circulating fan I blow slightly upward and aimed at the corner generate upward flowing air to help draw cooler air into my cabinet (the fan is close to where the biggest gap I leave is) and help break the temperature inversion. The lights create that inversion because they blow air outward around themselves trapping hot air below the hot air adding heat to heat.
The lights themselves will last longer if the cooling is improved.
Should give the girls a bit more tolerance to heat if you can keep their soil temps a bit lower too so I highly suggest getting some form of circulation going and drawing your heat from above and cool air from below...keep the heat flowing the right direction.
I hear Silica can also help the plant deal with higher temps without as much issue.
Hope that helped for now.
Will post pics if you still don't understand.