think it depends on the temperate of the car too?
like if youve been out in yours at 1.30am with a nice warm interior, leave it and its iced over at 5.30am when get up to go to work..
whereas if someoens cars been stood there since 5pm the previous evening it doesnt ice over as much??
im sur ei read somewhee that if you park your car up, leave windows open for 5/10mins so the inside gets as freezing as the outside, then shut windows and lock car up its not supposed to freeze over in the morning?