As a layman there are probably few theories behind this statement: 1. The plane is not an energy monolith, any part of the plane larger than the building (eg wi

As a layman there are probably few theories behind this statement: 1. The plane is not an energy monolith, any part of the plane larger than the building (eg wings) would have its own inertia which continues to rip off and around the building rather than drive all energy/mass attached to plane to the point of impact. 2. A smaller building may act like a plow if circular or hit on a corner, diverting energy as in 1. 3. If you simplify the side of a building to a supported plane, a larger plane may deform to failure more than a small plane due to the distance between supports ( other walls of building)