GSOB:
a HE shell (a kind Buk's warhead belongs to) produces expanding disk of striking elements. If time is applied then the hit cloud can be described as a cone.
Not true. With some idealization, the shrapnel forms a cylinder expanding in radius and height. It's neither disk nor cone. Anyway, the surface area is many hundreds of sq. m. depending on the distance from the explosion to the plane.
Shrapnel density is not high.