Head explosion doesn't work

[DomEReapeR]

So I've knocked out a church member in the junktown sewers, used Sparrow with a shotgun to bean bag their fatigue to 750 so they went unconscious, but now I keep using head explosion on them over and over and nothing happens. Any idea what's wrong?

[palathas]

Yeah, it seems Psionics are a bit broken. Using the same purple (psychokinetic) Psi-amp it does no damage on a critical hit with Psiblast, the basic attack.

[Platinawolf]

... I used the high-tech weapon that shoots ammo to give them a debuff that gives 200 fatigue per round for 3 rounds. I can reliably use Head Explode after it has done 800 fatigue damage. However, once they fall over, their heads are safe :(

[DomEReapeR]

Yeah I've given up on the achievement, every time someone reaches the fatigue needed for head explosion they're already unconscious and out of the fight, so it doesn't work anymore, infuriating.