For me I have not found the right analog stick's index. 2 and 3 are the trigger buttons, i started going up from there but didn't get a response so I stopped. Not sure if it's my controller (xbox360 wireless).
As for your original question (if you are still looking for an answer), Since the center of the stick is 0,0...
I was going to try getting the angle like this:
angle(0,0, Gamepad.Axis(0, 2), (Gamepad.Axis(0, 3))
also, i was going to trigger it with an "OR" block. So that it would only calculate it when the user was moving the stick beyond the dead zone. I had put in a custom dead zone for both axi. (rightAnalogDeadX) and (rightAnalogDeadY).
if right analog y axis is greater than "rightAnalogDeadY"
if right analog y axis is less than "-rightAnalogDeadY" (negative)
if right analog x axis is greater than "rightAnalogDeadX"
if right analog x axis is less than "-rightAnalogDeadX" (negative)