My tests have been closing in on 19 mm too. I have been giving this some thought and there could be some backlash involved too. Moving to a corner of the bed and back again can not be beneficial if there is a tendency to backlash.
There will be a lot of traffic cones in the end;
(I tried to find a CAD drawing of the cooling block at github but I was lost when there is no obvious naming scheme of the files.)
