The thread isn't about pulling or pushing. It's about having two fans and two exhausts out of the roof rather than having one. He has one exhaust system that pushes(or pulls) air out from the reflector and out of the attic. He has another one just for his carbon filter. He's trying to combine them so he doesn't have TWO holes in his roof. That's how I understand it.
As for my input, if it ain't broke don't fix it. Sounds like your system is maximizing air flow and maintaining good efficiency. Is there a problem with your two holes in the roof?
Putting the hot/warm air from the reflector through the filter doesn't sound like an awesome idea. I know that a lot of people simply vent their whole grow room through their reflector, but usually not through a filter. Hope that helps.
