As soon as a missile is in the air as many and as frequently as possible. Of course this only works if it's an IR missile and not anything radar-guided. The MiG could have fired either so spit out everything, dive for the deck, and pray.
RWR symbol radial position is based on relative threat. An M close is decided by the system as more threatening as an M in the outer ring. How it seems to go down in video games is to be roughly correlated with range and/or signal strength.
