Fine resolution of Image {X,Y} Position attributes for PixelMap Layer

I'm trying to set up an cue that has a live fade of a still image across an array of pixelmap'd fixtures. My difficulty is that the X axis translation of the image is very jumpy. At first I assumed that my problem was the 8-bit resolution of the (IPBC) Master where I had recorded the parameter value. However, I now believe that the Position attributes have only 201 steps, less than 8 bit.

It would be wonderful to have this issue diagnosed properly. I would be happy to provide a demonstration show file and happier still to beta test a solution.