DM Q&A: Mechanics: Coup de Grace?

[EDM Neo]

Not entirly sure if this is the best place to ask this, but meh... it's a question, and DMs can answer it. How exactly do coup de graces work in NWN? I understand they're supposed to take a full round action against a helpless (unconcious, sleeping, paralyzed, etc) opponent... but I can never figure out how to actually do it. I've paralyzed plenty of opponents, but I've only been able to coup de grace some of them, seemingly at random. How exactly do you perform one?

[Quadhund/Greenhouse]

It is automatically done with an attack action, but will only be applied to enemies with fewer than 4 hit dice.

[EDM Neo]

Thanks, I guess... I presume this is a balance thing? According to www.d20srd.org/srd/combat/combatModifiers.htm#coupdeGrace, there shouldn't be such a limit... then again, the standard rules are designed for player characters versus monsters or NPCs, not PCs vs PCs.

[Quadhund/Greenhouse]

I am pretty sure it is a NWN mechanic.