This change happened some months ago -- AA TPAC awards with BA miles used to be fantastic value (which unfortunately I never got to take advantage of myself).

I do take issue with this a bit, since it's not clear that BA does give AA the YQ, given that AA doesn't collect it from AAdvantage redemptions. If AA gets the money, fair enough. If not, this is at the very least disingenious, if not fraud. However, it has been discussed many times before.

But to actually answer the OP's question: you're not making an Aadvantage redemption, you are making a BA miles (or if post 16 Nov -- Avios) redemption, and the rules of that programme apply, regardless of metal flown.

tb

PS welcome to FT