By my experience (or maybe I'm doing it wrong) it doesn't work in closer ranges either....
12nm or less (even had did it with a target at 3nm just 3 days ago)...
STT mode.. 120 enabled.... target locked. I'm at their six....
I fire... wait for a few secs (up to 10sec max), turn off radar , and vector hard away from target (f-pole i think this is called).
No joy every time.
it seems like everytime I use the 120 without maintaining a target lock for the duration of the missle flight time, it will miss everytime.
Keeping a contant target lock is nuts, because now everyone on the other team now tracks me easily and shoots me down easily.