SmoothDamp or Lerp with Rootmotion to match a target position

Hi there. So I know this is a bit of a longshot but I figured I'd ask anyway.

I'm having trouble finding away to make SmoothDamp (or Lerp) adjust a float in the Animator so that a character moving via root motion can stay on position of a moving target and not over shoot it. In other words, the character needs to adjust the speed of the root motion running/sprinting animation to try to keep up with the moving target. If it helps my animator's Locomotion State blendtree my thresholds are;

 0.2f walk
 0.5f jog
 1.0f run
 1.5f sprint
 2.0f fullsprint

The threshold is controlled by a 'Speed' float variable and I need to adjust that so that the character will stay on target.

Hopefully that makes sense.

Is there a preferred solution to this sort of thing? I'm sure I can't be the only one that's doing this.

thanks David