Just thought I'd pop in and share this after nearly going crazy. I've been downloading alot fo the mods ported from FO3 like crazy and only recently realized my hair was clipping through headgear like the red goggled ranger helm and the batman cowl to name examples. I thought I'd screwed something up and finally found the Biped Data Flags in the armors while looking through FONV Edit. Now some of these full covering helmets/headgear had the 'Hat' flag on them which regardless of also having the 'Hair/Headband/Eyeglasses/Mask' flagged makes the cropped hat hair show and clipping through the back and/or top. So if you're having this trouble with helmets it may be a cause.