On Asiamiles, you will only be upgraded on CX sectors. It does not involve other oneworld carriers, even if there is BA involved as you cannot mix carriers when using an upgrade award. If you want to be upgraded on BA, then your reservation needs to be entirely on BA. FYI - on BA, you will be upgraded to Business Class. Not World Traveller Plus.

You will be using Zone D award.

You will still be credited with the miles for economy class travel toward Asiamiles.