Interesting.

All i will say is that some of the higher octane branded fuels are boosted with ethanol in order to achieve the higher octane rating.

Optimal stoichiometric air-fuel ratio as we know is 14.7 part air to 1 part petrol.

Stoic for ethanol is 9:1.

Obviously running marginal ethanol in the mix is going to have a negative effect on MPG Vs a pure 98 Octane petrol with lambda set to get as close to 1 as you will see on the MOT or what that translates to = 14.7.