Came up with the ATAN2 solution that was really needed to limit instructions. I have a much more performance conscientious end result.
IN screenshot format, this is the angle to use:
The material function at the end is literally the IF statement I have been using al along - packed into a function that takes a 0-1 value to clip it. The angle is fed into it to generate the rotation.
You can see my full material on this vid:
