Set analysis using dates/derived dates that allow all filters apart from date

[Russ]

Hi - I have a KPI that shows case count for this week to date from yesterday vs the same period last week (e.g. if today is Friday, show Mon-Thu for this week vs Mon-Thu last week). I also have a date dimension used on a chart called Month-Day that allows drilling down from month to day and is based on the derived fields of LinkDate (e.g. LinkDate.MonthYear)

I have the following formula for the set analysis which is part of a pick statement (pick uses either PROD or ALL for WhenFoundFlag):

count({<tblName={'Opened'},[Case.WhenFoundFlag]={'Prod'}, LinkDate={">=$(=WeekStart(Today(),-1))<=$(=Date(Today()-8,'MM/DD/YYYY'))"}>} DISTINCT Case.Id)

It seems to pull in the right number, but need to be able to allow it to be filtered by any filters (there are many), but not by the date. When I select a previous month on the chart, it changes the KPI, even though the set analysis is fixed on previous WTD - any ideas on how to do this?

Thanks!