I am sure this is covered elsewhere but couldn't find anything

I'm doing a lot of JAL domestic at the moment,and company policy is Flex Y (B fare class) so that I can catch earlier or later flights as needed. 20TPs per segment.

At airport check-in, there is nearly always a payable upgrade to J available for around 2000JPY (around £12 at current exchange rates). That earns me an additional 20TPs, or a rate of £0.55 per additonal TP.

Fill your boots.