This is just a speculative question at the moment, but I'm looking for a future year to travel to Tahiti. Not worried about a TP run, but would like to get TP/Avios as best as possible.

AA codeshare on Ait Tahiti Nui, and so an example flight could be

02 MAR LHR -> LAX BA283
03 MAR LAX -> PPT AA7177

Now this is a FAQ question I'm sure, but how do I book the second flight on ba.com, if I use multi city it says no flights available, but matrix gave it as an option? Is it because its an AA codeshare that it doesn't work?

Finally, is this actually the best route?