Since it was hot and I knew that I was going to be pushing the limits on Monday, I drove a bit more conservatively on the way to/from work. I don't recall what the center display read when I got home, but it reported 6.9 mi/kWh for the trip in (which is a few hundred feet downhill over 13.5 mi). That's better than normal, but in warmer weather I am routinely above 6.
Here's the rub, though: that trip used 10% of the battery, and 13.5/(28.9 x 0.10) = 4.7 mi/kWh.
IOW, as pessimistic as the GOM is about range, the efficiency numbers reported by the car are overly optimistic. However, I also don't think that going by % of battery is perfectly accurate either (although it is clearly better), as there seem be some non-linearities/anomalies there as well.
To paraphrase the wise old owl, how far can an F56 SE go on a single charge? The world may never know...