Not quite. The 18% autogratuity is charged on everything ordered a la carte, but not on the prix fixe menu. So, as a platinum cruiser, if you order only the prix fixe menu and apply the $45 platinum credit to cover that, there should be no added autogratuity. If you order additional items, even as simple as bottled water, the 18% is added for the extra costs. In theory, you could get by with a $0 bill (only ordering prix fixe), to which you would add your additional gratuity for the server. We never manage to do it this way ourselves for dinner, but have done the brunch that way multiple times. Our platinum daughter who cruises solo does it for Palo dinner every cruise, since she doesn’t drink and loves the selections on the prix fixe menu. She tells me she tips $10-15 depending on the quality of service, so the $10-20 per person for this sounds like it’s right in line.