I think your numbers illustrate what I was talking about with more Wh/km the longer you ride. I assume the first 3/4 of your ride was on battery one. That included the time you were fresh with energy. By the time you started on battery two, you were fading in energy levels, a bit slower and using more Wh/km
Ghost pedaling? Is that even possible on a torque sensed bike? With a big heavy rig like mine and torque sensing, I don't know as I would make it up some of the hills near the end of a long ride. When the hills get steep, my bike is often more efficient ghost pedaling than putting my effort in. I have seen the time when I was pulling 1,450 watts from the battery plus my pathetic effort and going 4.5 mph (7.2kph). Dropping to a lower gear and ghost pedaling where the chainring spins at 120 rpm+ got me 6mph (9.6kph) at the same 1,450 watts battery draw.