Cognos 11 calculating percentage of calculated columns isn't showing the right #

[zgeorge]

Cognos masters,

I have a list report that is calculating MTD sales and Prior Year MTD. This is calculated by the following:
aggregate(if([Actual Agreement Sales].[Time].[Full Date] between [First of Month] and [Date Prompt Cast]) then ([Actual Sales Amount]) else (0))
aggregate(if([Actual Agreement Sales].[Time].[Full Date] between [First of Month Prior Year] and [User Date Prior Year]) then ([Actual Sales Amount]) else (0))

I also have a column that is calculating Actual vs. Prior Year. When I simply do the [MTD Sales]/[MTD Sales Prior Year], I get the correct results for some rows and incorrect values for other rows. I have also found that the INCORRECT ones are when the row is summing up multiple rows. And the CORRECT ones are the ones with only one line instead of multiple summed up.

Any help on this would be greatly appreciated.

Best,
Zach George