3x Skyrim Dragon Priest masks in different sizes, should work for 6'' figures and up to 7'' MOTUC sized heads.
Width point of the smallest mask is up to 15.5 mm on it's widest area (around eye height).
Width of medium one is 17.8 mm
And the Large one is 19.8 mm wide at it's widest point.
You can order them in various plastics but due to the small size of the details, I would recommend the Acrylic plastics or the Frosted detail types which come with a better finish and detail quality than the regular white strong and flexible.