[css-flexbox] aspect ratio question

https://drafts.csswg.org/css-flexbox/#hypothetical-main-size

My question is about item B in that section. Why is it limited to a
used flex basis of content? If I specify flex-basis: 50%, but the
flexbox has an indefinite main size (-> flex basis is not content, but
we also don't hit case A), then we should not use the aspect ratio if
we have one?

Are there other values than an indefinite percentage (or auto and
content) that should be matched by this? My understanding is that
anything else would hit A, is that right?

Thank you!
-Christian