I'm having all my windows replaced - professionally, so, not a DIY. This was prompted by the fact that on all of my smaller dual pane windows (~36x48), the outer glass (if it's glass) appears to be caved in, or bowed in, so much so that I have determined the outer sheet of glass is touching the inner sheet of glass. (Last winter I had 1/4" layer of ice on the inside in the middle of the window where the glass sheets touch.) Walking through my subdivision, I see dozens of windows with this same effect. Is there a dual pane strategy where the outer sheet of glass (or whatever) is intentionally formed not flat?