... If you live in London/Europe you may wish to join BAEC and credit to that program instead. If you are in business/first class on the CX flights, you would get enough miles for a short-haul flight or several on BA; and perhaps if you do the calculations it may turn out to be more worthwhile to credit the whole ticket to BA.
Keep in mind, if you want to "qualify" for status at BA, you will need to fly 4 segments/year on BA metal.