Cover currently do represent the opening level of windows, garages, etc. So if a cover is at 100%, it means that a window is completely uncovered or open. However from the meaning of a cover in my understanding a cover should represent the coverage level, so that 100% are representing a fully covered window, garage, etc.
Imagine the slider range of a cover is completely grey if the slider is set to 0%. The grey line represents the possible way a cover can move when leaving the storage box. By moving the slider the range between 0% and selected value becomes colored (by default blue). This colored range in my opinion should represent the desired coverage level of a window and not the desired remaining opening level.