I went back between 91° and 90° and read limited information on the internet. Having now made a few miter folds I wish I had gone with 90°, 91 leaves more clearance than I like on the back and requires extra effort to ensure your part doesn't kink while gluing. I could be wrong as this was my first midfold test. I may get 90 bits in the future, but it's an expensive learning experience.