if you don't wait for the amraam to pitbull before breaking lock, you reduce the Pk of the missile quite signifcantly coz its basing its last known target info from the launching aircraft's radar, it'll fly blind for awhile.... then when the missile finally goes pitbull, there is a chance that it might not acquire the target if its out of its onboard radar scan cone......so it'll go stupid.... worse it might lock on to the first target it sees........
unfortunately, if u wait for the amraam to pitbull, chances of getting killed by the other guy is also much higher.