Move value to a different week in set analysis

[Seppe]

Hi all, 

I would like to have values move in the week dimension of a table.  As an example if a supplier grants 30,60,90 days more or less payment terms, to see what effect that would have in the cashflow per week.  

So : if vAdditionalSupplierTermDays variable is set to 30, we should add 30 days to the date so that the corresponding cash value is moved further out 4 weeks.  I have the following set analyis.  It shows the values, but there is no shift in weeks.  

Sum({<InvoiceType={'Supplier Invoice','Customer CN'},
%Date={"=%Date-$(vAdditionalSupplierTermDays)"},
AlreadyPaid={0},InvoiceState-={'paid','cancel'}>}[_OpenInvoiceAmount])

Thanks,

Seppe