I've never had any luck with asking for volunteers .... ;-]
I spent some time looking into it because it was a challenge. That may be enough to get someone to try it and if they do it and can document it they'll get bragging rights for their accomplishment. On both the '15 and '19 it's with larger tires I found the average MPG to being very close to matching my spread sheet calculations. The spread sheet logs the vans miles between tanks and uses a fixed percent to estimate to come up with a calculated miles per tank. It uses the same percent mark up for the van's odometer to get a calculated miles on the van. The percent markup was come up with by using a GPS to track actual miles traveled verses what was on the trip meter and odometer. If you do that with the stock tires you'll find the van's odometer is off by one or two percent anyway. I think +/- 2% is the industry standard.
For me the bottom line is I can live with the odometer and speedometer being off as long as it can be tracked for maintenance intervals. What I like about the way it is with the larger tires is the average MPG is close to being accurate. That works for me because that's not something I can estimate in my head while driving down road.
There is also no way to know how the vans multitude of modules linked by the CAN bus uses tire size in whatever form it's in, where it (or they) are stored. Another possible issue is the "Ignition Counter" getting reset" when doing the PCM Module initialization / relearn vehicle data procedure. As far as what I've read online, you do have to do the relearn procedure for any changes in the tire size to get picked up and put to use.
My wagon with around 3500mi on it has started this very abrupt downshift/clunk/jerk when letting off throttle and slowing. Never had it happen until shortly after a full throttle application- which also downshifted hard. Reading up on it the downshift clunk is very common in other applications...
www.fordtransitusaforum.com
Edited to add .... sportcoupe Can you post a screen print of the new settings for Tire Circumference?