Hi,
Either you calculate your dither so that there is still a low stiction, then the regulation loop is improved, because the stiction error is smaller than before. But ther still remains an error.
Or you calculate dither so that the valve continously moves (with dither frequency) around its optimal position. This causes best regulation results. Ther is no hysteresis you need to compensate, and the errir is about zero.
The problem is that the steady movement will wear out the valve. You need to replace it in a relativeky short maintenance period.
Maybe there is a way to switch dither on when needed, and off the othef time....
Klaus