Stomp hit is determined by chance?

I thought for sure it worked like this:

• Enemy executes stomp
  • If target is inside certain radius, target gets hit for full damage
  • If target is inside a larger certain radius and is running, target gets hit for lighter damage

Am i wrong and was it really was chance-based according to distance?

I've been wondering the same thing...I've always believed it to be proximity-based.