Can't get above 35mpg- something wrong?

Chat member BlauerClaus published charts (for the Gen III Prius) showing the affects of speed and temperature with and without air-conditioning on mpg. There is a significant drop off in MPG due to the lower density of the air once the air temperature goes above 90 degrees F.
His post can be found at: Fuel Economy diagram with and without Air Condition | PriusChat

I'm looking at the speed/temp/consumption MPG without air conditioning graph to take out the AC variable and I'm not seeing the significant drop off in MPG above 90 degrees F.

No MPG numbers are decreasing as you go from the last two rows of data for 97F to 104F temps. There are a 15 columns (out of 25) of data that have the same MPG on those last two rows, which seem to indicate that MPG will not increase much (may even decrease) above 104F. But I would not call it a significant drop off (I call it too hot). The MPG numbers are increasing just fine at the 90F temp row of data, and all rows show an increase at 97F, over the 90F row.

One thing to remember is that his graphs are based on simulators. They cannot account for everything. My main argument is that rolling resistance due to lower air density and especially tires is where this bump in efficiency comes from despite lower oxygen density or density altitude if you will. From 100F to 40F tire rolling resistance can nearly double. A little extra horsepower is not going to overcome such a large jump in rolling resistance.

Check the first graph (no AC) again anyway and you'll see there is no drop off in mpg as temps rise. In fact, at 59-62mph the mpg continues to rise.

Has the op actually ever reset the fuel economy gauge? Or is he still running on the original average? If the dealer had left the car stationary for any length of time with the car warming up, or even if the op leaves the car to idle or warm up, then that will seriously affect the average.

Perhaps he could confirm and maybe reset the mpg's at next fill up?