It depends on the exact fare class, but presuming you bought the cheapest ticket you could find and BA was offering the deep discount fares for Christmas (they don't to CPT but might to NBO), no plan will give you more than 50% miles and most are 25% ... so it isn't a lot of miles to fuss over. Booking an AA codeshare typically doubles the fare, but gets you 100% miles (so you decide if it is worth the cost). Similarly on BA booking WT+ (their premium economy) would get you a bigger seat as well as 110% miles (also lets you join BAEC as that is a qualifying fare). The pricing for WT+ varies widely with route and season (but typically not cheap around Christmas!).

All of the OW FF plans are distinguishing between deep discounted and not so deep discounted fares now, not that much difference in shopping around. BAEC not even letting you join with a discounted fare (even an expensive one!) clearly indicates what BA wants from its FF program.