Exactly - you can lose power going low, but rarely get it by going higher.I remember either Modern Motor or Wheels tested the 760 Turbo Volvo when it was new.
Initially they couldn't work out why the acceleration numbers were the same as the NA version. Turned out someone had fueled it up with standard petrol. Once they put premium fuel in it the Turbo version delivered the performance that it was renowned for at the time.
So if you in this case anyway, the wrong fuel meant it lost a lot of power.