I don't think the range numbers mean so much at all. In fact, what I'm seeing is that when you start with a lower number at 100% charge, the car appears to need less of the apparent range to accomplish the same drive (or at least one not too dissimilar). Take my drive today, for example - left home with 100% charge and 89 available miles showing, arrived at the office (30.5 miles later) 67% charged with 64 miles showing. Almost the entire run was at 65mph with cruise on, thanks to the MLK holiday.
Now, on the surface of things, that would appear to be a pretty good run - I only "used" 25 miles worth of range, but it also appears I'm on target to go from 4 bars used to 5 bars used on the SOC meter in my usual spot (within a couple of miles from leaving work). If the car stays on 4 bars used for a fair bit longer, then I've actually done better. I have my doubts that will happen.
Here are the previous (not too dissimilar) drives. Probably drive 2 is the closest to today's - I remember that as being a light Friday morning where, again, I barely had to have the cruise off. But that (unfortunately) sort of skews the data, because the most similar results were not only under the same driving conditions, but I also started out with a similar reduced amount of range. It would have been better to have that same kind of drive on a day when I was ~100 miles apparent:
1 - Left home with 100% and 105 miles showing. Arrived at the office 67% charged with 60 miles showing
2 - Left home with 100% and 90 miles showing. Arrived at the office 67% charged with 58 miles showing
3 - Left home with 100% and 99 miles showing. Arrived at the office 67% charged with 57 miles showing