BA 757s always used to have a lower "Max FL" than FMC due CAA v FAA diffs, or even the whim of one BA Fleet Manager - we had a chart on the back of the FMC reflecting the Max FL we were to use (as above, increased buffet margin).
Bear in mind that the RFL is likely determind by a (bought in?) piece of software - costly and time consuming to alter. Changing Max FL by CP dictat can be achieved overnight, and tweaked (as here, 1.5g to 1.45g) by immediate experience even ATC feedback....
Someone speaks well of BA and RFL, but we often "tanker" fuel (especially post Buncefield) that is not on our Flight Plan, hence lower Max / RFL. Believe it caused some problems, especially ex USA, in the early days with Atlantic crossings all at lower levels than filed...
Only solution I can really see is better comms / heads up... ATC asking / crews advising early when RFL is not as filed...
NoD