Always pull air when possible. IT is much more efficient.
I doubt you need an intake fan at all. The exhaust will pull air through the intake passively.
You also want to have more power int he exhaust so that negative pressure is created which is how fresh air gets drawn in. Put the exhaust at the top of the tent and the intake on the opposite side on the bottom. Intake should be twice the size of the exhaust.
I agree with you 100% MYOB. But I think his problem is that he has not too many openings to take the air from. He stated that the air intake opening is from a vent outside. If he could it would be great to make more openings so that he could take it in passively. But he's only working with one opening (I'm assuming its too small to do passive intake until he tells us the duct diameters he's working with) , the vent register coming from outside of the attic, as he implied.
I'm definitely not arguing with you MYOB. I'm a proponent of the passive intake / constant exhaust scenario. I've actually agreed with you quite a few in times in other threads. But if he only has the one opening for intake air, then he will not be able to do passive intake unless his duct can be sized accordingly. Which might be possible.
P.S. if he has no choice but to do a forced air intake (because a duct for the intake cannot be upsized for passive) then the fan is more efficient pushing air through the beginning of the 9' duct with the influent side of the intake fan unrestricted by a ducted connection.