Does the vent need to be plastered in a cold roof?
I think most people here with two full floors have a cold roof, i.e. the insulation is right on the concrete ceiling. Have you plastered the vent in the batten area?
I've been looking at this since yesterday and for some reason I can't figure it out. As far as I can tell, ventilation at the transition to masonry is not required if the vapor barrier is installed. But I don't know if that is true.