Take a look at the picture I placed here a few posts earlier. If you crank open the skinny window, and the two bars that extend the window are right next to each other, there is no spacer to cut. When you crank open the window, the bars extend and get closer together so there is no gap between them that can be reduced.
I only found one window (in the bedroom) of my Windsport that was too thin to modify. All the others (two different sizes) were modified and I can open them much further than originally.
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