If you don't need to stop at the ticket/checkin counter then going from either the A side or the B side to security/trams is like going from the side grandstand to a goal post of a football stadium
Now, if the Magical Express dropoff is not exactly centered (think: you enter a stadium not at the 50 yard line) then one security station will of course be further away then the other.
Each security station handles half of the A side and half of the B side.
Back when DME had dropoffs on both sides, many guests could get to security more quickly by getting off at the first stop as opposed to "their side" but had to go to "their side" to get their bags back from under the bus.