The % setting of the cell will depend on chlorine loss because that is the chlorine you are replacing every day.

Also, SWG cells are usually rated in amp-hours. So it is both the time the cell is on and the current running through the cells. Higher salt levels creates more chlorine but also higher amps (Goldline cells) and it is somewhat linear so that should be a wash because the higher chlorine levels means a reduced run-time (%).

Cell life seems to also be dependent on the chemistry balance. This is why some SWG owners experience very short cell life while others are much longer.