In trigonometry, a counterclockwise rotation is positive and that is the way atan2 works, as you can see in this link: http://en.wikipedia.org/wiki/Atan2 . I guess you can modify the function in the way you want. Try this to see if this solve your problem:
« NEG R->C ARG »
or if you want:
« -> x y 'ARG(x-i*y)' ->NUM »