Seems to me it might be ... and I'm not a mechanic by any means, but ....

You've got the blower forcing air into the motor, but the air upstream of the blower is relying on atmospheric pressure to get TO the blower. So it makes a lot of sense to me that anything you do to ease the route from outside through the pipes and tubes and filter is going to help to some degree.

We need a staff scientist to prove out this theory. Any takers?