Not sure if you mean 6.0 mpg with Vitesse throttled at 9 but I average 16-18 with it at 9. Once you get used to it you learn how to drive smoothly with it at 9. I've had it at 5 also which is still very good but I like the option to punch it if needed
Now I see what you mean..lol...that 6.0 mpg was when I reset the MPG and did a quick 0-60 test run. But my normal daily drive with it a 9 gives me 16-18 mpg.