When MLs ask for tips in exchange for extras I hardly call that a tip, it's basically off-the-books payment for a service like hiring your plumber friend to fix your toilet for a massive cash discount.

If we were to properly tip an ML it would've been the same way we'd tip waitstaff in the US - the tipping culture there is based on empathy for the waitstaff that are getting paid low base wages.

Seeing how most MLs are making lots of money from behind the door extras, the only time we'd feel like tipping extra money is when we feel like the ML is not making enough money for the day. Sometimes the ML is excellent but she just doesn't provide DFK, BBBJ/CBJ or FS only NHJ so it would be appropriate if the punter tipped extra when the ML provided an excellent heartfelt session - maybe she listened to his heart being poured out the whole session without being interrupted or judged as there are stories of punters who book sex workers not purely for the sex but mostly for the pillow talk their wives won't give them the time of day to.