When to ask for a decrease in PM cost?

[Winn Merwin]

Hello BP,

My wife and I currently have 4 doors/3 properties with a PM who we really like. We are currently paying 10%/mo. 

We are under contract on a 4 unit property. I am wondering when is it appropriate to ask for a reduction in monthly % paid to our PM? Is 8 units enough? Total should be about 6K in gross rents when they are all occupied. 

Should I ask for a reduced rate on the new ones? Reduced rate on all of them or wait until we have more properties?

Thanks in advance.