[chriswep]

the more likely explanation seems to me that not all panels were hit by a sufficiently large hailstone to cause an initial break. once the structural integrity of a panel is broken, smaller stones can damage it further that wouldn't have otherwise..

[gpm]

Probably not just the size of the hail that hit it, but where the big pieces hit it. At a first guess they're using tempered glass, and that's a lot more likely to fracture if you hit it near the corners than the centre.