If you provide only one specification, and you want to include 99.73% of your measurements, you do not need to change the 6 to a 3. Minitab divides the number by 2 for these calculations.
Enter the default significance level that Minitab uses to remove the interaction term from the model. Minitab uses this option only with the ANOVA method. The default value is 0.05. Minitab also uses this value for Evaluate Measurement Process (EMP Crossed).
Use a higher significance level, such as 0.10 or 0.25, if you want to be more likely to keep the interaction in the model. Use a lower significance level, such as 0.01, to be less likely to keep the interaction in the model.