Based on Dan's post, it seems like your math makes sense. Sorry I don't know more to offer advice.
I just looked into it and do not think it actually makes sense for me.
With AA, i can fly TYO-HKG-JFK in F for 62.5k pp.
With BA, it would be 20/30k in J/F TYO-HKG and then 105k HKG-JFK pp.
Don't think it makes sense to use all those extra miles pp. I also happen to have a lot of AA from this past summers Citi Exec fun.