Yesterday I did a 77 mile trip on ECO mode, then on the return journey I was in NORMAL mode. The journey was 75% motorway, the rest being mostly 'A' roads mainly with a speed limit of 70, but some at 50. It was light rain both journeys. Outward journey I kept at 70 all the time using cruise control, coming back I was late for a meeting so drove a bit faster, 75+.
Outward journey 37.8, back was 37.5.
So hardly any difference and with the faster journey coming back I expected to be 35-36, but it was only a very small amount less.
It's probably fair to say a mainly motorway journey is not the best option to use a ECO v NORMAL comparison check, but I still expected a bigger difference. I don't think I did anything else to affect the result, and the conditions were identical.
I will do another some time, but maybe I will try none motorway.
Odd result that.