I'm gonna guess because I don't know s**t about what is happening during a snap but here it goes. The smaller stab needs less yawing of the fuse to remove the air flow from it and the unstalled side has less surface area due to i'ts smaller size therefor can not control pitch by it's self. The larger stabs need the fuse to yaw further in order for it blanket that stab from air flow, the side that is in the airflow is large enough to still control pitch on it's own to a point. Ok jsut my guess.