That option really only works on models that are flying wings, deltas or use short span wings such as semi scale jet fighter style wings with wide spaced stabilizers. Otherwise the natural damping of the wings fight the roll effect from the elevons very strongly. In the case of the foam glider that AA5BY is using the roll authourity would more than likely be rather dismal as the wings are more than high enough an aspect ratio to fight the roll from tail surfaces and reduce the control effect to far below what would be acceptable.