I also have a 14 REX. My batt kappa max went to ~13.1, or 70.2%. I took it to the dealer and they "updated the software" and I'm back to 16.1ish.
Here's a thread with a little real-world info. https://www.mybmwi3.com/forum/viewtopic.php?f=11&t=5651
I'm nervous about my battery capacity. I...