For the ask about Mulan cosplay, I would think that the reason for not fitting someone's view of what "Asian" should look like as a Tsinoy (Chinese/Filipino) is different from the reason for a Hapa. For a Hapa it may be that you don't look Asian "enough," but for someone who is of Southeast Asian descent it's more that we aren't the "right type" of Asian. But the same principle stands: They're trying to define you thru their own narrow-minded experiences, so don't let them tell you what you are.