Ventilation duct size with reducer

Hi all, I have a 6 inch inline fan and an air-cooled reflector with 8 inch duct flange, and I plan to use an 8" to 6" reducer to connect them. I can't decide if it's better to run 8" duct through the system or 6" duct. Does it make more sense to set it up like

fan > reducer > 8" duct > reflector
or
fan > 6" duct > reducer > reflector

I also have a 6" carbon filter on the other side of the light and same question applies there. Thanks.

run the 8 duct if you can manage the bends. use the 6 if you need to make turns you cant do with the 8. 8 will be quieter as well as more efficient.

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