S4-Arch

My windshield has started to crack from the edge right in front of the driver. Crack is under the windshield wiper, from the edge of the glass. Dealer says no to replacement, caused by rock. I don't see how a rock could curve under windshield wiper, over hood edge to get to the window with enough force to crack windshield. Wondering how many windshields have been replaced under warranty? circumstances? tia.