Confused about two scenarios-Dimensional Reporting

[cognos05]

A report showing inactive accounts and accounts are inactive if last 2 months qty sold are 0 and prior last 3 months had sales qty.

Filter on Accounts : TopCount(filter(filter(Descendants(set([EAST]),[Distributor Sales].[Ship To Customer].[Ship To Customer].[Customer]),tuple([Qty],[Last3Months])>0),tuple([Qty],[Last2MonthsSales])=0),5,[Total])

SO I have to do these for different products from different levels, so add a prompt with product members from different level and used the prompt in slicer of the main query.
Everything works fine here.

Now if I remove the prompt expression in slicer and put it inside the tuple, then my inactive accounts are not properly filtered and get some accounts which has sales in last 2 months also. so basically something happened to filter, is it because the tuple is confused with which level the prompt value belongs or I really dont get the reason, but would like to know.

Expression used :
TopCount(filter(filter(Descendants(set([EAST]),[Distributor Sales].[Ship To Customer].[Ship To Customer].[Customer]),tuple(#prompt('prmProduct','mun','[Items]')#,[Qty],[Last3Months])>0),tuple(#prompt('prmProduct','mun','[Items]')#,[Qty],[DecisionStatus])=0),5,[Total])


Thanks,
Nithya