Nice try on the testing, having the second set of "A" runs drop off makes the test invalid in my option. The temps dropping may have played a factor.
What were the winds like?
Can you try it on a back country road? I have a 2 mile test track here that is .5 mile acceleration, 1 mile test, then .5 mile coast down. Turn around and repeat. This makes the test a lot shorter which helps by taking less time, giving less time for the environment to change, less gas is used testing, easier to toss out a run if a car passes or similar.
You can also try a coast down test, it will not give you a MPG gain but will give a % aerodynamic improvement.
Just some ideas
Once you get good data I will add it to our wiki:
Grill block partial or full - EcoModder