You may find that the difference in price between a FC through fare and a ticket with a broken fare, FC to BKK and then business class to BRU, is small or even negative. Also, in such cases, airlines tend to argue that the downgrade compensation should ba based on the most expensive unrestricted and fully refundable walk up fare, as if you had purchased a FULL J/C ticket at the airport just before departure, rather than as if you had bought the cheapest business class ticket what was available when you booked your flights.[/QUOTE]

Even so...you are then pricing a fully refundable walk up fare in F Class to one in J class. There still is a big difference there as the ticket has no dollar value, only points.