I couldn't post Spritmonitor because of not having enough posts: anyway I also filled up with V-Power in Luxemburg, it's about € 0,22 cheaper. The high record of 31,6KM/L I was not able to maintain, perhaps also because I got my airco condensor fixed and I can imagine it hurts fuel economy a bit when your car is being fixed.
The last two fillings where both 29KM/L but that's combined use, where when I set the record: it was only highway and not city roads at all. I must say though, the price in Belgium has been going up and it hasn't go down anymore.
https://www.spritmonitor.de/en/detail/915384.html