Hi Scott,
I am not mapping a repeating / tileable surface.
My assumption is that Flow Along Surface is doing some interpolation to the target surface in UV space. I would like to know if there is a way to control a bias with respect to the UV space mapping so that the pattern is, for example, tighter in the U direction on one end of the surface and wider on the other. This would allow one to compensate for a surface that dramatically changes dimensions from one end to the other and maintain a (mostly) square U to V spacing relationship as shown below:
Again, I am using a square grid to represent interpolated UV values (0.0, 0.1, 0.2, etc.) but the pattern I am mapping is non-repeating.