[@Hekazu]

I think the way it works is that when the enemy [i]attempts[/i] to leave your reach. I emphasis attempt because there's plenty of reasons why the enemy may not leave your reach, such as you tripling, grappeling, or killing them when they try. In this instance, the AoP, if taken, occurs before the escape attempt does. It's only when it fails to stop or does t occur is when the enemy is free to continue their movement.

To put it in another way, do we retcon Brannor's AoP because he effectively killed his guy, since he also didn't leave Brannor's reach?