When putting this on your door how much shorter should the double rail be from the actual door
Welcome to the Bunnings Workshop community @Kayesmith. It's wonderful to have you join us, and many thanks for your question about the Flexi-storage over door hook.
That all depends on what length double slot wall strip you're using. They come in a variety of sizes. The strip itself can run almost to the bottom of the door if you wish, but you need to consider the kick panel's height to the bottom shelf. If you have the rail past this point, it will bump into the bottom of the cupboard and obstruct the door from closing.
Please let me know if you have further questions.Mitchell