I have a 190cfm fan 4" and my tent is 2.5x2.5 x 5ft high. I only have 1 passive intake open about 3 inches. Only thing i can think is there isnt enough negative pressure to cycle the humid air out. Or it could just be since the window is closed its pulling the humidity right back in. Take a humidity meter and set it somewhere near the tent when you know the humidity is high in there and see whatvit is outside and around. If outside air is lower like say 50% and its 75 in the tent you need less passive intake open space.