I never communicated any of those things. 
I was thinking it was like a tithe and goodwill.

chaoticalHeavy

But the initial bump in compensation resulted in an initial bump in service quality. How to maintain the service quality increase?

Perhaps the problem with tipping is that the expectation is not clearly stated: at least when I tip, I don't say things like, "I'm giving you this tip because you did x and y, and I appreciated x and y. If you do x and y next time I will also give this tip next time."

spirituality

My experiment with over tipping

But the initial bump in compensation resulted in an initial bump in service quality. How to maintain the service quality increase? 

Perhaps the problem with tipping is that the expectation is not clearly stated: at least when I tip, I don't say things like, "I'm giving you this tip because you did x and y, and I appreciated x and y. If you do x and y next time I will also give this tip next time."