I'm guessing maybe the audio taper (or reverse taper), the A or C on this graph might have given you a better result with the steps. I truthfully didn't think of what you experienced when you bought these. I'm still a little confused about the wide range of values, what exactly does the circuit look like that's feeding the A/D? Is there some loading we're not taking into account? Maybe using a lower value pot would have minimized any loading effects.
