Yes, stop using the scale in that way. The cup fits a shape, not a size. Your cup size is determined by taking the difference between your band and bust measurements... but those measurements, in and of themselves, are gonna vary, because the shape of a breast and position of the nipples etc, is different from girl to girl. At the end of the day, what makes the difference, tends to be how bulbous the shape of your breast is. Frankly... as bulbous as Ashley's are, despite being so small and close to the torso, it's actually possible she is a D, just with a 26 band size or some shit like that.
I've personally seen a 26 E, while doing research to make sure I wasn't talking out of my ass here, and she looks kinda flat. In fact, boutiques she went to had all told her she was somewhere in a AA-A range, like around the size of the girl from Ex Machina. But you can clearly tell her breasts were more round than that. It's more likely, the boutiques were trying to fit her into something they had in stock to make a sale. Because when she went out for custom bras, they're like, yeah no, you need a 26E. Lo and behold, to top of the cup stopped being empty, and the wire actually sat comfortably beneath her bust, keeping the band in place, stopping it from riding up over her nipples when she moved her arms or resettled in a chair or whatever.
In short, you've all been lied to, cup has been used as a shorrthand in a way it wasn't meant to, and it stuck, to the point that the people who make money selling them can't even get it right.