The problem with a fixed amount of aileron to rudder mix is that the Cub wants a lot of rudder when flying near stall speed but not so much when cruising at a high speed. Push the elevator forward to unload the wing and it wants no rudder at all. Load the wing negatively in inverted flight and the rudder needs to be opposite of the ailerons. It's best to just learn to use the left stick on your radio while you fly instead of relying on mix to do it for you.

All planes, not just Cubs, need rudder for a co-ordinated turn. Practice using the rudder even on planes that "don't need" rudder and you will become a much better pilot.