Regarding handling with a lighter trailer: My former trailer was about 7 feet longer and 500 pounds or so heavier. I don't notice any difference towing on the highway unless it is windy. Then it is obvious. The shorter trailer is also much easier to navigate in gas stations, campgrounds, etc. where tight turns are involved.
I agree that fuel calculators need to be verified.
We had a 2003 Toyota Camry that typically showed 32 mpg average, but calculated to about 30. The speedometer also showed faster than the Garmin GPS by about 2-3 mph.
My F-150 seems to be pretty close. Sometimes a tank will be off by up to 0.5 mpg, but it is possible that I didn't refill to the exact level. That is close enough for a retired government worker.