We are planning a 7-day on Navigator of the Seas in July and plan to take most meals in the main dining room. We will also be tipping at least the suggested amounts for Waiter, Asst. Waiter, etc. We also plan to take one meal in Chops for which the extra charge is $20/person. Is a "standard" 20% ($4.00/person) appropriate for this "prix fixe" service or should a different amount be left...OR is the service in this restaurant considered part of the "regular" service?