The other factor is the defrost vent is in the middle. So perhaps the effects from the windshield impact is made worse by more extreme temp delta? In that lower center portion?I have started to save pics of cracked windscreens. Out of the 27 I have collected, more than 50% look similar to yours. This simply can not be coincidence. Not sure how to proceed, if at all. My first broken screen looks identical. very frustrating!