They're the only PM so they can charge what they want, I'd say. They manage a lot of properties 150km north of their agency - they add an extra 11% for that town.
I worked it out on mine to be around 20%, with 15% just being the weekly fee. That's enough of a hit to make me really want to self-manage, as I'd rather have the house making MONEY for me (or have someone buy it, which is more money)