If I go to a restaurant and buy a bowl of corn chowder and a glass of water, the restaurant is into me for $6. Let's say I give the standard of 20% - that gets you $1.20. I'm not the kind of asshole who tips coins, which means I'm tipping $2. You're getting a 33% tip for bringing me two things and we're both feeling ripped off - you because I only left $2 and me because fully 1/4 of my meal price was your surly, unthankful service.
If I go to the same restaurant and buy the surf'n'turf and a flute of roederer, the restaurant is into me for $85. Let's say I give the standard of 20% - that gets you $17. You've still brought me two things - but now you're making $8.50 per serving vessel. Yer damn skippy you're happy - you made "case of beer money" bringing me two damn things. Me? Well, there's no kind of service you can legally give me that will make me happy, particularly since in order to drink that glass of roederer over we involved the sommelier who I also have to tip.
It makes more sense to tip at Subway than it does to tip at Spago. At a 5star the guy who brings me my food is just bringing me my food. At Subway I'm determining if I want e.coli or not.
Pay an hourly wage that makes sense, just like the rest of the world. If I think you went above and beyond, I'll slip you a little something. Otherwise just f'ing figure it into the cost of the food.