I have a feeling there may be some "random fragmentation" involved too. I have been bombed & sent to tower while in a GV - I see the bomb hit, think to myself I'll be ok, it was a ways off. Then I hear metal on metal clang & *tower*
I have also been near the edge of an incline (small ones even) & the bomb hits on the other side of this & it's very VERY close to me, but I survive.
ANd I have been close to an impact, think "I'm toast" & survive...but no clang
My point is, I think there are a few variables to the "blast radius" besides just - How large a circle around the bomb impact area does damage.