I think that you're right, there is no way to answer what you're asking without discussing personal tipping habits.
If you are at a sit down eatery in Disney and have a party of 6 or more where you would pay an auto gratuity, the auto gratuity is 18% no matter what. There is no designation between buffets or menu restaurants.
If you are a party of 6 or less the recommended amounts are the same, regardless if you're at a buffet or a menu restaurant. At any restaurant, with a party of 6 or less, you can tip whatever you feel appropriate.
I can't think of one restaurant that you would only encounter bus boys at Disney, so that'd be a non-issue when planning your trip.
(Auto gratuities would also apply if you're using the Tables in Wonderland Discount Card, regardless of party size.)
Outside of Disney's rules, what you tip is entirely up to you and isn't up for discussion, debate or judgement on the Restaurant Board.
Hope this helps.