Duncan Budapest

I have a problem tweening and using progress on a bezier curve http://codepen.io/DuncanBudapest/pen/pxdgF I hope the codepen makes the situation clear. In the code the object 'steps' around the curve. As I understand progress represents the complete tween so any position can be represented by 0 to 1. In my example my total progress is 0.5 but the object tweens to 75% of the track. In the complete code there are multiple objects and there is some degree of control using the timeline. I've stripped the code down to make it easier to understand.