You've got it right. The air displaced has to have an outlet when refilling, and air has to come itno the cart when printing to replace ink used in the printing process. The maze is covered, I would guess, to slow evaporation in the sponge area. I have refilled empty aftermarket bci-6 carts (high quality from MIS) that had an air vent over the sponge but did not have a maze or cover. Worked just fine.