Quick answer: The dial should be no more than two clicks off center in either direction.

Long answer: Set it for a good transition. But it's true that the break in should be done before the final setting is done (at least two gallons). It's really easy to set so you can do it many times during break in. Just set it in the middle to start. Run the engine up to clear out the fuel in the engine. Then let it idle at around 2500 RPM or less for about 15 seconds. Go to full throttle as fast as you can. If it spits fuel or smokes it's too rich. Turn the low end dial clockwise. If it dies or bogs with no smoke, it's lean. Turn the dial counterclockwise. When it can idle for 30 seconds or more and transition quickly it's good to go.

Important: The dial is very sensitive, basically you cannot turn it in small enough increments. It takes some skill to find the perfect spot since you may go past it a few times. Once you get used to tweaking it in very small movements it's gets easier. You should be able to see the "ballpark" area on the dial where it works the best and remember this (write it down). Then keep tweaking it to get it perfect. Once it's set after break in it's good for a long time.