Good question, but I am as puzzled as you are. What I do is remove the headrests, use the smallest vacuum attachment to vacuum the rear area, and than just do the best I can to wipe clean the rear window. The bottom portion of the rear window really doesn’t block the rear view, but it sure pisses me off when I know that I could not reach the bottom portion. Next time, I will try to wrap something thin with paper towel and see if I can get most of the area clean.