Hi there ash22,
I was trying to do the same thing, so that the sweep started at 12 o’clock and went around clockwise.
I ended up creating my own custom material function but copying half the VectorToRadialValue function. However, I adjusted some of the math at the beginning so that it produced the results I wanted.
Note that the TexCoord values are -2 and -2, and the scalar being subtracted from it is -1.
I have also swapped the mask G and R around into the x and y inputs to the atan2 node.
The atan2 node is a custom node, and the code is return (atan2(y,x)); with an output type of CMOT Float 1 and 2 inputs, named x and y.
Enjoy 