I think of the ball whack comparison to taking up the slack of my skin in the heel chord barbell scenario.  I literally have no extra skin to work with.  So when I ball whack my skin I feel nothing changing really.  Same with smashing my heel chord against the barbell.  When I say “hurt” I mean more like tender tissue pain — you know the pain cave.  I feel like as I go along with mobilization I know what normal tissue feels like.  I would say my heel chord feels normal, but when I go in the position of restriction such as down in a squat I have very very tight skin and hard muscle right around the ankle/heel.  It feels like there should be more sliding surface there to give me more room.