As far as talking air flow, if your intake fan and/or booster fan have a lower cfm rating then your exhaust fan, then your exhaust fans air movement is being restricted because of it. This is why many people will recommend a passive intake system and strong exhaust fans. However, not sure of the details on your fans. If possibly, I recommend basically giving every single detail that you could possibly think would play a role in whatever issue you're have, whether in the case or any future threads, as limited info results in limited ability to give good results.
However, there is also a great search tool here on RIU that can help track down other threads involving high temps to. Thinking the height of the space is going to continue to challenge you as far as turning your light up higher. Other option to consider, would be completely removing current fans, sealing the whole space, and using co2 to help the plants thrive in higher temps? Again, the search tool can be very helpful.