we came up with our PM fee by taking our number of flips per year. taking the profit. taking what we thought was a fair salary, and turning it into a percentage of profits. For example if we made 100$ in year 1 and the PM could handle that volume working 40 hours a week and 10$ was fair compensation, we turned it into 10%. That way the PM's interests are aligned with your own, and thats making as many dollars on the rehabs quickly.
Also it may be rough comparing your percentage to other PM's because the profit equation may be different. For example, we take out hard money costs whereas another flipper here in town does not soooooo, the profit is a much different number.
I give her phat bonuses because she's amazing and really makes the machine run.
Also, think of your PM job as you learning the rehabbing process inside and outside so you can eventually do them yourself without being employed. Its an extremely expensive education you are getting.