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I FIGGURED IT OUT ANONS, I SOLVED THE MYSTERY BEHIND ANYA'S TITS
Its not that she has one or the other as a default.
Her tits only become enlarged when she gets horny. She starts producing large amounts of milk when she starts to get in the mood for procreation, thus creating the swelling in her chest.
After they are enlarged she will have to spend some time milking herself to reduce their size so that she can fit her small body back into her clothes without bursting out and breaking them.
she is only flat when she is not horny, that is why she was always embarrassed to show them off during her earlier streams, because she knew someone would notice sooner or later, and she is using a binding or lots of bandaging wrapped around her chest to make sure she doesn't swell during streams.