Trying to create a hair mod that works with hats

[ModBrains]

So I'm trying to follow that (very old) tutorial on making a hair NIF that works with hats.

I have a single NIF file that has two meshes - one is hat, the other is nohat.

I have two egm files, named Hairhat and Hairnohat.

The textures are in place.

I have made an esp that assigns the hairstyle to the appropriate race/gender.

I have made sure the esp was activates when testing the file.

If anyone has experience in getting this particular thing working, I'd appreciate being able to pick your brain on this.