Oil Level and Fuel Economy

[MadMax]

Not talking about weight savings (which would be nominal at best), nor keeping the oil level below the minimum amount (any fool knows that's not a good idea).

What I was wondering was if the Yaris ran more efficiently with the oil level at the halfway point or slightly below versus at the upper levels. I know in the oil change thread it states it is better not to fill it up past the mid-way point, just wondering if there was a fuel-efficiency reason for that...