[smileysteve]

difference in theoretically versus practically.

Bigger vehicles have bigger engines, frame rails, and suspensions. Some of these for cost, some of these for towing performance.

An example being a truck, bigger frame rails that will crumple less, leaf spring suspension that will crumple less, and a high rake grill that will capture more force, and a higher mounted engine and higher mounted passenger compartment that makes separation less ideal.