Good write up, believable info & data.
Have seen 23 on a full tank day trip, but under 'ideal' conditions and less than cop attracting speeds.
Back at the mpg ranch, I would have a difficult time doing our usual 'runs' to NJ/NY etc., at that kind of low(er) speed and the attendant attention/process necessary to obtain better than our 'usual' mpg, trip-wise. Couple that with our high rpm at speed 5 spd manual, and it simply 'is what it is' for us in our '01 X.
For fun/curiosity, I have done some full tank conservative speed/careful driving 'trips' in our '02 VetteVert, and our best was 33 point something, over nearly 600 miles. That car is our 'econo car' in almost any usage.
GL, mD