How much negative pressure are we talkin here, for your tent? Is it tight if you pull at it? You need to remember that unless your tent is in a lightproof room, come flower, you're going to have to close any vents, which will only increase temps. I've tried all sorts of different layouts with my equipment. I settled on active 4" 210 intake with a 6 inch 440 pulling through the filter, blowing through my light, and exhausting outside. I found that turning that 6inch fan down to about 50%, reducing negative pressure while still maintaining it, along with the intake from the active intake, gave me the best results. For some reason, when I had the 6inch fan turned all the way up and my tent was sucking in on itself, it was hotter. My theory is, under that kind of pressure, the air is going to flow from point a to point b (point b being exhaust) without having time to disperse in the tent. in other words, a turbulent airflow was created, like a vortex of air, if that makes sense. That's my theory anyway
If you have variable speed control on your intake fan, try turning it down and getting the pressure down so the air going in isn't immediately sucked out. Counter-intuitive I know, but worth a shot.