Ok so I think I've figured it out. Dodging strike has the increased range if you are facing the enemy that attacked your shadow. So even if they are not in the path of the attack if you are facing a way to get to them you will go to where they are directionally, so up, down, left or right of them. In the sentry fight you have lots of wisps that have random paths and are typically not near you so you just end up going past the sentry because they can be on the other side of it after their shot hits your shadow.