Airport Station Transfers

Do the Silver Line buses that stop at Airport station stop behind the Blue Line fare gates, or would I have to exit the fare gates from the Blue Line to transfer to Silver, or go through them if transferring the other way? I'm curious because I've gone past Airport Station on the Blue Line a couple times in the last month, and considered making that transfer to get back to South Station instead of going back to Aquarium and walking from there. To be clear, I want to know if the Silver Line buses are behind the fare gates so I know whether to tap my CharlieCard when I get on to register the transfer if outside the gates, or if I can just board the bus behind the fare gates and take my seat, like at South Station and the underground stops in Seaport. Just want to plan ahead because I'm planning to go to Revere Beach more times this month.