Cut down 15mm and flare the outside face of the guide 11mm out allowing for free entry of the curtain from the head box.
File, grind or cut the internal webs at the top as shown to allow free unobstructed flow of the curtain into the guide.
Please Note: When making the 15mm Flare, use thick cardboard to protect the surface of the guide, from being scratched by the vice grips.