Remember that "opposite aileron" while inverted will be in the same direction as the rudder. If you enter the spin with right rudder then right aileron will be opposite. Also the direction you spin has a small effect on models due to gyroscopics, for an upright flat spin with left rudder and you'll get a little "flatter" spin... inverted flat use right rudder. On full size the direction of spin is the only way you get the spin flat at all... if you spin upright to the right and add power the nose will actually drop and the spin will rotate faster.