Nocturne QoL Buff

His E gives him bonus movement speed against "Fleeing" targets but what it means is he gains bonus movement speed against units with the CC of Flee on them, what if he gained it if the enemy was simply moving away from him, sort of like a reverse Cassiopeia ult (But a MS boost not a stun, duh). And would it be too overwhelming to have it stack on itself, even if it's with reduced effectiveness?