In my upcoming mod, El Karan av Umarile, I'm trying to turn Umaril's head into a helmet. I thought it would be relatively simple because he already looked human, but I'm having unexpected issues with it.

When I equip it onto an NPC in the CS, it looks normal from about the cheeks up, but then below that line the mesh stretches out to some vanishing point underneath the NPC's model. I can post screenshots from NIFSkope and the CS if that helps, so if somebody could help me get this mod working, that would be great.