creating a calculated member in mx

Hello, please when I use the tail and nonempty function on rows it gives the correct value for the member (query below)select {[Measures].[Vol]} on columns,tail(nonempty ( [Dates].[Month Short Name].[Month Short Name].allmembers),6).item(1) on rows from[ICS];----------------------------but when I try creating a calculated member with similar expression it gives the result for the whole set instead of the member (the query is below )WITH MEMBER[Measures].[Value]AS(tail(nonempty ( [Measures].[Vol],[Dates].[Month Short Name].[Month Short Name].allmembers),6).item(1)) select [Measures].[Value] on 0 from [ICS]please any advice