I will agree that a little extra goes much further with the server at the local diner. But thats also bc that server is more likely to have a regular customer base than the one at an expensive place. Unless you are a regular customer, the server has no idea if you are a good tipper or a lousy one.By coffee shop, I'm referring to what other areas of the country might call a diner or a greasy spoon, not a Starbucks. Nor do I tip over the counter workers regardless of how Starbucks chooses to describe them to try and convince me they're something they are not. But I also don't order drinks with 20 hidden menu items and make their lives miserable on the very few times I go into a Starbucks either. If I did, yeah, I'd give em a tip.
Yes, the expensive restaurant has bus boys, food runners, and the like. So in fact the waiter himself is actually doing less work than the girl at the coffee shop who in many cases is doing all of those things herself. But the work done for me, is about the same whether it is done by one person or by three in total. There may be drinks or an extra course at the expensive place. But again it isn't 10 times the work. And regardless of how it is split, the waiter himself is going to end up with more total out of that than the waitress at the greasy spoon. And a little extra goes a longer way with her. So yeah. I'll go to much higher percentages above 20 much more readily at the cheap end.
But it is an entirely different category of service between the local diner and someplace that runs 100/pp. Servers don't interact with there customers the same, they don't deliver food the same. There is a much higher expectation of service at a fine dining place than at Denny's. And Denny's has bus ppl, hostesses, food runners too. Denny's server's probably run more because of the table turnover they'd have, but per table the high end place has far more that they do for a table than Denny's does.