The small wings are called Canalizers. Their function is to smooth out the airflow leaving the prop before it hits the tail. This should reduce the amount of required right thrust and increase rudder authority. You should set it to zero degrees and then adjust based on what is observed during knife edge flight. That said, they work best when the airplane is completely dialed in. Your CG and incidence settings need to be spot on before the potential of having them is really noticed. I suggest you get the airplane dialed in really well without it then add it to see if you realize a difference or not.