Regardless of how it ran for the last 15 flights the high end should be dialed in whenever you go to the field. Weather changes and so does the settings. You can fly all night on a certian setting, but did you ever notice (here in the northeast any way) that as the sun starts to go down, the drop in temp is just enough to make the dew drop, along with barometric pressures and the engine that ran fine all evening, is now too lean. Also as some one else mentioned, you will notice differences as it breaks in. Joe