Collision impulses: static mesh vs physics asset

I have two physics driven actors which I drop from the same height: a static mesh and a ragdoll, both have the same weight of 0.7 Kg. I print out the “NormalImpulse” value they receive when the ComponentHit event occurs. The results are a bit confusing: On landing the static mesh’s greatest impulse (from the series of events produced when it hits the ground) is around 600 while the physics asset reports 80-100. Is this a bug?