The white area appears to be getting brighter because we are seeing it more directly. Looking at it obliquely it's more faded much like looking at the sun on the horizon is more faded that when overhead because we are looking obliquely through the atmosphere. Look at the orientation of the debris ring. The dimmer view of the planet is more oblique. The white area also appears the same size going down to the same general latitude, it just looks bigger when you can see more of it.