I think the key word here is frequent acceleration and this is a major cause of higher fuel consumption.
My belief is that if you are on a freeway and you need to overtake then this will cause the fuel efficiency to drop. By using Eco Mode then the performance will be reduced and this will aid fuel consumption.
However, on a freeway, the level of regeneration is also reduced so the benefit of the hybrid system will not be realised and this won't boost economy.
I would keep it in Eco and see how you get on, maybe switch between the two to see any difference on the economy read out