I am using direct contact between the nozzle on an aluminum build plate as my z probe (electrically closed loop). As the nozzle comes down, some plastic is being expelled out of the nozzle and as it touches the bed underneath, it cools down instantly. The nozzle needs to push through and remelt the cooled plastic in order to create contact with the bed. By issuing a G30 that could move horizontally as well as vertically, I expect that the cold extrusion would clear out to the side as the nozzle approach, thus preventing the associated bed distortion.