You're welcome to break this down however you wish. I don't think there's any perfect measurement or stat here as every consumer values the various components of the combo differently. If you are a consumer that values the drink highly, then a dog-only analysis is incomplete. If you only care about the dog then you want to leave the drink out. Neither of these calculations is inherently more or less accurate than the other, they're just relevant to different preferences.

My original point is that by changing what metric and how much of the combo you look at the calculated loss can vary significantly: over an order of magnitude difference between the dog-only volume loss and the refilled drink calorie loss.

lies, damned lies, and statistics.

And some people eat the dog dry and some add a bunch of relish and mustard and four other toppings. And some people don't eat the bun. And some people don't even finsh the dog. So what?

The option to get water is a meaningless observation that doesn't invalidate the assessment of what you get for the money.