One key that helped me finally “get it” was to keep my hands in the “palm up” rotation. Rather than a bicep curl you are doing sort of a forward raise motion, you should wind up upside down with your feet on the wall and your hands over your head in position for the glide. My tendancy before was to try and turn my hands down so I could grab more water to help with the flip, but then the hands come out wrong for the glide. Good flip turns finish with the push off upside down, weak ones tend to try and flip over to the stomach before or during the push off. Try transitioning from free into backstroke on the turn. I’m no fish but this has worked for me.