I want to see you try to measure your shoulder blades

Its about being comfortable and not closing up your chest by having a bar that's too narrow.
IDK the 'correct' way to measure. I feel comfortable on a 44 which is pretty close to outside to outside of my shoulder but that is kind of a tough measurement to take accurately. From edge shoulder bone to the other pulling tape across my collarbone is 39cm. IDK if any of that helps you