Think about it this way, too.
You go to an expensive restaurant, and get treated as you should. You are served your beverages, your order is taken, your appetizer and meal served, your dishes cleared, your coffee poured, etc. Your bill comes and you pay $145 for the meal.
or
You go to an inexpensive restaurant, and get treated as you should. You are served your beverages, your order is taken, your appetizer and meal served, your dishes cleared, your coffee poured, etc. Your bill comes and you pay $45 for the meal.
Did the server at the expensive restaurant work any harder or any more than the server working at the less expensive restaurant? It takes the same amount of effort for the server to fill your glass with ice at each restaurant. So why should the server at the high-end place be rewarded with a big fat tip just because the total for the check is higher?
Presuming that you use 20% as your guideline, the server at the expensive place gets $29.00 dollars for the effort, while the server at the inexpensive place gets $9.00 for the effort.
Lesson learned. If you work in a restaurant, make sure it is the high dollar one.