All the illustrations I can find of these muscles have the shoulder extended, with the arm hanging down, and the stated function of the rotators makes sense intuitively in this configuration.
When the shoulder is flexed, with arm reaching vertically above the head, it seems that the 120 degree movement of the humerous relative to the scapula would change the geometry of the rotators so that they don't work in the same way as they do with the shoulder extended. Do the rotators still work as stated with the shoulder flexed? If so, how? If not, which muscles perform internal and external humeral rotation under shoulder flexion?
An illustration that depicts the answer intuitively would be greatly appreciated!