Quick question with no pics, but hopefully I can describe it. If not, I can grab some photos later. Anyway, what causes the skirt on the sides of a jacket to buckle or fold outward instead of adhering to the sides of the hips? Some of my jackets do this and I need a vent strap, others don't and I can't figure out why that is? Would it be the height of the vent or a different kind of canvas used on one vs. the other? Thanks!