The angle variance centered on the sides of the platform. Zero angle only matches sides 90-degree to the platform "top".
Increasing thesideAngleVariance
allows the definition of what is a "side" to be expanded beyond the surfaces perpendicular to the platform "top". For instance, if the Effector2D source was a CircleCollider2D then the sides could be set to an arc on either side of the circle.
See Also: sideBounce, sideFriction.