I agree with your suggestion, but my extraction fan moves the RH down in less than 3 seconds, so the extraction setup so far is overkill even with the ducting loss. In fact, I had to restrict the input opening to less than 10% in order to make the RH reduction this slow.
I think the overkill extract setup will be, if not completely necessary, at least handy once the unit gets hit with a couple pounds of wet bud at a time. Even with only about a pound of wet bud, the extract fan was initially turning on every 8 seconds or so to bump the humidity down. With a lot bigger load, it will need even more extraction, but given that the RH is reduced so easily now, I doubt that the extract fan will ever be needed to stay on for very long each cycle.
Anyway, thanks for your observation, I am always interested in design ideas that might be helpful.