Im pretty sure, looking at the pictures of the vango that its like all the other air awnings and doesnt have a rear air pole. The beams to use the correct term come out from the awing rail, over the top and down the front with some sort of cross member centrally in the awing. At the rear is a thick bumper pad, you can add a steel pole to these on some models and these pads are pulled tight against the van by the pegging system. Even many of the old porches were of this type of construction.
To answer your question, though not ideal as the windows scratch easily, i guess most of us have had to do this at one time or another. I have just bought the Kampa 390 because I wanted a large size and almost certainly part of my window will be covered by the bumber pad.