LiteTween: how do I calculate progress for sprite position?

Imagine a sprite moving from x=0 to x=1000 with LiteTween easeOutCubic function. It starts very fast, then slows down.

I want to manually place the sprite at x=200 and then continue the tween as if it started from x=0.

I know about the Seek action, but it requires progress (from 0 to 1).

I can't set progress to 0.2 because the function is not linear. For easeOutCubic the progress at x=200 will be something like 0.072

So how do I calculate the correct progress for any given position of the sprite? Or is there a way to tell LiteTween to resume at current position, not at current progress?