From my understanding tuners are using the o2 censors for calibration on the flex fuel tunes. Working in conjunction with the fuel level and telling the system to read o2 inputs after a fill-up for a specific amount of time...
Or something to that affect..
Yes, if there is a 10% change in fuel level(or less if you change it), the car will recheck it's E percentage based on how much fuel is needed to achieve lambda 1.
Update to HPTuners v3.0 and the flex fuel tables will be there. You can use the tables from the F150 coyote to start with. Just be sure to check all your flex fuel tables to be sure they are okay.