The last three days moored in Barcelona a surge began to wave us back and forth along the sea wall to which we were tied. This caused an uncomfortable jerk at the end of each cycle, so we modified the aftermost dock lines as shown above.

Rather than run them from the stern corners where the angle of dock line to our hull was acute, we moved them about ten feet/three meters forward. This attenuated the snap with each surge cycle to the point where it was not noticeable. Should we find ourselves in a Med mooring situation again this will  now be the standard rigging system.