GRJ: You may be right about the different tapers. The low and high ends of these linear pots have a tighter range of values. It would be interesting to try the others just to see what comes out.
I'm satisfied that these will do the job. Just a bit of a surprise that the spacing is so uneven. I plan to check some of the others from the lot that I got from Mouser. I expect that they will behave in a similar fashion.