Im sorry, I don't get it.

Why does the 3rd person need to be in CE for a 45min flight?

Unless BA release Avios space, any alternative way to get into CE will be suboptimal. ie book Economy and then change later (£35 fee).

Seems illogical behaviour for very small gain.

Anyway, each to their own. Hope you have a good trip. Edinburgh is lovely, and they have a Hawksmoor now as well