This is how i am set up.

Box fan > wire shelf with 2 miners & psu (1 per shelf) > (6" fan adapter > 6" insulated duct)/miner= 2 exhaust ducts.

I was looking at introducing the y to combine the exhaust ducts with inline booster fan to push exhaust added distance, but I think I'd have to increase duct size rather than continue with 6" duct.  So rather than the 6x6x6 y i would need 6x6x8  or 6x6x10 with appropriate booster.

Last night i tried lengthened ducting to make curve out window on one line.  = fan speed increased and temps rose slightly.  I'll add booster and try that tonight.