I've made the PW mechanism possible to close window opening from 20 cm (7,9") to app 24 cm (9,5").

Since I've got little to compare with, and I cant wait to to this because I need to put the doorskins together with the door frames again.

I do know that the total, vertical high on a Du Vall winscreen is app 20,5cm (8,1") in the middle, on top of the cowl.
However, the low edge on the sidewindows are much lower than the top of the cowl. But on the other side, rods with Duvall screen always have a canvas top which goes around the corners and a little down along each side of the windscreen.