Here is an extract from some of my correspondence with the FPS
If they decide to medically discharge you, what you get depends upon, for AFPS 75 members, your rank for pension and your length of service and, for AFPS 05 members, your length of service, final pensionable salary and the Tier they put you in.
If they administratively discharge you for not meeting medical standards you would only get an AFPS 75 pension paid straight away if you had reached the Immediate Pension Point. AFPS 05 members would get a preserved pension but may get an EDP if they had reached the 18/40 point.