Not true - as we know from a bad experience. We relied on that once :-(
Canvas shrinks more after being agitated in hot water too, I'm just taking a break from ironing thirty metres of cotton canvas for the new structure. it will be worth it, we don't want the problems we had last time.
Indeed. That's why it's important to keep a flysheet away from an inner tent.
Mary wearing two hats - tentmaker and camper :-)