The map can have alot to do with it. More aggressive fueling and boost etc...
My v4 type R gets 220-230 odd at best out of about 50 litres, and sometimes more near to 200 depending on how I drive it! Obviously even less on the track
(342 BHP).
My bug get 290-330 depending. (270BHP).
Not sure if your RB5 has a bigger fuel tank than my classic but that might be what is helping? Seems very good economy for the power yours is running.