could possibly be coz you're using vpower... i think it's 98 octane, so it's a bit more efficient. when i had my mitsu verada kr, it had done 420clicks. i was using 10%ethanol for a while, but then switched to 98octane (whether bp, caltex or vpower, whatever) after a friend told me it was more efficient. i never figured out which was actually cheaper, as i never did a L/100km test with the e10 fuel, but after switching i made around 10-11L/100kms, lots of highway driving, but 40-50km/h highway driving (stupid peak hr traffic ), and as well as that the car was much more responsive.
that's with a 3L v6 verada