Bearing in mind that the missile can tell which is the front of an aircraft and which is the rear (from simple temperature differentials) then aiming for the cockpit is as "simple" as as "look at the hottest portion but actually aim for 15 feet [or whatever] in front of that"... The warhead goes off aimed at where the cockpit is likely to be. Any built-in lead, so that the missile doesn't simply chase the aircraft, which has been the case anyway since just after AAMs were introduced (e.g. lead-collision) then the aim-off (offset) accounts for the difference in position between cockpit from exhaust nozzle. Oh, and I'm STILL waiting for some reference to these supposed KE (zero-warhead) anti-aircraft missiles you claimed.