Calculated Measures using Case or IIF statement and not getting correct Subtotals on Pivot tables.

I have the following Calculated measure -CREATE MEMBER CURRENTCUBE.[Measures].[Act - Fcst Lbs] AS case when [Measures].[Act- Fcst Flag]= 0 then [Measures].[Invoiced Pounds] else [Measures].[DMP - Forecast Lbs] end, FORMAT_STRING = "$#,##0;($#,##0)", VISIBLE = 1 , DISPLAY_FOLDER = 'Calcs' , ASSOCIATED_MEASURE_GROUP = 'DMP Forecast'; works great. however when I display with our calendar hierarchy Dimension, the months will display the correct values, but the subtotal on Year will not be correct. I know its because the calculation is occurring on the Year line. I've tried a Scope statement to override the year, which works IF you select all the months in the year. but if you select just a couple, then the total is not correct.If the source if the values were not in 2 different places I'd take care of this in the SQL source table.Our Calendar Dimension Hierarchy is as follows[Calendar].[Fiscal],[Fiscal Year].[Fiscal Month] Any directed would be grateful