ScaleME, if you use the covering to twist in the washout by shrinking it in then it'll tend to pivot the wing along a midline based on all the springiness of each element of the wing. So the actual pivot point will be somewhere around the wing spar but probably not centered on it. A D tube type wing will tend to pivot around the very stiff D tube somewhere in the center of the shape but towards the spar location.

Of course if you jig build the wing with the washout built in then you can have complete control of where it goes but it's not really neccesary.