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			I only have to chop mine when it is cold, as when warm it fold properly.   
 
I have always thought that if you could stich in a solid re-inforcement at the top of the window, this would prevent the vertical crease from forming and the top would drop properly.  It wouldn't have to be big, just a think metal bar, which could be covered in fabric. 
 
Just a thought.. 
 
Mike
		 
		
		
		
		
		
		
		
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