A terminal transfer ticket from the machine or ticket office is the same price - $5.80. There is no reason to use the ticket office.
The station access fee you refer to applies when using Opal or when purchasing a non-transfer ticket. I don't think this has ever been applied to terminal transfer tickets.
At one time it used to be a much higher cost from the ticket machine. It used to be $5 from the ticket office and around $13 from the machines.
At one time, the discount rate was only supposed to be charged to those that showed a ticket for flight departing from the other terminals and so had to be purchased from the ticket office