Romeo fit was one of the configurations cleared for the F3 Alarm capability. There were various different configurations to provide flexibility for the mission planners. With Romeo the 1500 Ltr was on the shoulder pylon. This allowed 2 AIM 120/Sky Flash to be carried under the fuselage on the other side. 2 Alarms could be carried on the inner wing pylons with 4 AIM 132 on the stubs.
Can't recall but I think you had to jettison the 1500 Ltr prior to firing the AIM 120s. I'm sure someone who was on 11 Sqn at the time can recall all of the info?