Maybe this video will help you: https://www.youtube.com/watch

Hi Farip, I can tell you from my own experience that the overhang of the box over the windscreen adjusts itself depending on the length of the roof box and the roof. The first time I tried to mount the box, I mounted it too far back so that I could no longer fully open the tailgate of my estate car. For subsequent installations, it was more important to me to be able to open the tailgate fully and to accept any flow noise or loss of aerodynamics. By the way, my luggage compartment is completely occupied by the double dog box - that's why I stow the entire luggage of 4 adults and 2 dogs in my XT L box ;-)