Do you only have one green "ECO" light? I have three of them, the more economic I drive, the more light up. The lower light is red and lights up while accelerating more than about 25 %. Beside that, there are some other differences, too.
Yesterday evening I drove 50 kilometers more with my girlfriend and lights switched on. To hold the average fuel consumption under 3.4 l/100 km I had to drive slower than 70 kph most time, but that are still amazing numbers.