Tiny_Sly

I do have to add that this is my answer for 1.12.2 but it should ALSO work for future versions.

I know this was posted almost 3 years ago but this is for anyone who is still looking for an answer. First, find your config folder. -> C:\Users\ (desktop user's name) \curseforge(or the application where you've downloaded you mod)\minecraft\Instances\config (The config folder should be in the same folder as your mods folder.) Once you click on the config folder, search for CustomNpcs.cfg. Once found, click on it (you can edit it using notepad) and search for the line "headweartype". Set the value to 0 if you want a 2d head layer, set it to 1 for a 3d head layer. Then save the options and you should be good to go from there! :)