I've come to a conclusion: There is no kill threshold. Whether a hunter killer crashes or blows up is all RNG, and this was proven when I shot at a ninja seeker with a craft charger laser which is the weakest craft weapon ever. Guess what? It still blew up. It was destined to blow up. No matter how little damage you do, it will always blow up. The only thing you can do is pray that the next ninja seeker you see is set to crash and not blow up. But just keep in mind that you might be waiting for years, because I've gone through plenty of space missions already and I still have yet to see a single guild spaceman because apparently the Academy (and the occasional killer droids) has a monopoly on space.