You folks are more generous than I. I don't pay a full 15%-20% when there is no order taking and no food delivery. Busing I consider a standard task, just as I expect the floor to have been swept and the restrooms clean.

So paying a full tip for less than full service would be a disservice to professional waiters who do their job well.

Me, I leave a tip similar to what I'd give for wait-service at a table at a bar. Maybe a buck or two more.