Ok, an update - the tank was about half-emtpy at 103.3 miles. I filled it up last night to the FIRST CLICK ONLY and the amount filled was 4.940 gallons.
So I achieved 20.9mpg on the last 103.3 miles.
Now, I did take the car on a few extra jaunts around town out of necessity in the 103.3 miles without considering the affect on my test.
I also filled it with premium gas last night and the fill-up previous to last night.
Lastly, I removed the K&N filter from the stock airbox about 25 miles ago and added a Fram filter from Walmart.