I see the only one way to handle this is if the MMS would collect total amount outside the room and signal the providers with thumb up. They would not know the amount until after, then all services would have to be the same. I can choose to add on after if you wish. I believe this is fair. New Image in Somerset used to collect just a flat total fee. No question of HF or Tip. Just "short stay" or "long say".
FYI: If you take $40 from $140, it is only 28%.
I don't feel sorry for the providers or feel guilty to tip $100, because they make more money than most people (unless you are doctors, lawyers, or own a football team). Minimum wage in NJ is $14.xxx. An Amazon driver is make about $20 hours or $200 for a 10-hour day. After tax, he/she would take home about $160. And no one can dispute that an Amazon driver is working very hard. These girls can make that much in 1.5 hours and sometime much more with their regulars and holidays.
From observing the models of cars on the lot, they are making more money than most of you mongers.
Just treat them with civility and you can come and go with a clear conscious. If you feel that you were mistreated with the standard tip, this is the forum. You have the MMS's ears.