If you have selected "Sum Forecasts" as one of the recalculation option you will likely get different IEAC values at summary levels as compared to computing the IEAC at that level with the performance data for that level. This option tells Empower to sum the IEAC values from the lower levels up to the summary levels rather than calculating it for the summary levels independantly. See section 15.2.1 of the Empower User's Manual for more details on what this option does.