I suffered with hangetsu. I have knee injuries and was taught to turn my knees inwards by my shotokan instuctor. I adopted the stance to focus more on my hips and abbs. After all the hips are the powerhouse for karate techinques. This made the kata more beaable, and the stances felt stronger. This is the way I now teach it to my students. From a physical point of view turning the knees inwards is not a natural motion, and could lead to ligament injury. Thanks for good point SaiFightMS