Weird energy consumption oddity.

I live in Florida and my area is completely flat. I commute to and from work on I-4. I also frequently drive to Orlando on I-4. Over several months, I have observed that my efficiency is worse when driving West to East and better when driving East to West. I usually blamed it on wind but today I put it to the test. Today it is very calm, no wind whatsoever. I drove approx. 27 miles from exit 28 in Lakeland to Exit 55 in Davenport. I had the cruse control set to 70 mph. and I reset the trip odometer upon entering the interstate. When exiting at exit 55, my efficiency showed 3.9 miles/kwh.
On the way back, I did exactly the same.. Upon entering I-4 at exit 55, I reset the trip odometer and when I exited at exit 28, my efficiency showed 4.2 miles/kwh.
I looked at topographic maps of the area and there is no significant change in altitude. There was no wind.. I have no idea how it is possible that CONSISTENTLY, my efficiency is different depending on the direction I drive on a completely flat highway..

Just to note, AC was OFF both ways and I was running WAZE via Android Auto.

 

I only spent 15 minutes there. Temperature difference was about 3 degrees.
I observe the same on my morning commute to work (east to west) and back home (west to east).
Despite the headlights being on in the morning, I always get .3 better efficiency going to work in the morning and worse at 3:30 pm when driving home. It is hotter on the way home.. (of course only comparing the efficiency with the AC off both ways.

 

It is hotter when I drive home from work compared to my commute to work in the morning and I get better efficiency in the morning. Today, it was hotter coming back from Davenport and I got better efficiency in the hotter temperature.
As far as I can tell, the altitude difference is less than 20 feet between highest and lowest point on the trip which should not make a difference.

 

It's not just at certain times.. It's consistently a worse efficiency when driving east compared to driving west on I4.... It's really weird..

 

I doubt that the temperature has anything to do with it. This phenomena happens every time. I wish that I could find a more detailed topographic map of I4 even though I doubt that this is the problem. One thing that impacts efficiency is the amount of traffic.. If there are more cars on the road, it does create some amount of suction, just like when you are tailgating.
I actually have observed exactly the same phenomena with my wife's gasoline van. Every time, we go to Houston and we travel on I-10 between Lake City/FL and Houston, the gas mileage going from Lake City to Houston on I-10 is at least 1 - 2 mpg better than going from Houston to Lake City. You start and end at about the same elevation. There are "hills" on I-10 and as you are not recovering lost energy on the way downhill, that may explain it. However, with an electric car, if you start and end at the same elevation, you should theoretically get the same efficiency going the same speed as your car will recover the energy it took to go up the hill when it is on it's way down.

 

Thanks.. I will try that..