From what I've found this seems to be the ideal setting to run in an ABC type engine. As an experiment I ran a brand new ABC slobbering rich for 45 minutes just to see what would happen to it. At the end of the 45 minutes I stripped it down to have a very close look. Far from causing any damage (and it was running very cool) the piston was totally unmarked and looked brand new while the liner was starting to get a polish. I then reassembled it and ran it for 20 minutes in the more accepted hot running and stripped it again. This time there was quite discernible wear on the piston. So the 4-2 break point would give about the best average between no running in and too much wear. "Wear" in this case means damage, not just getting the correct fit.