SSRS LYTD Calculations

Let's call it "Last Year to date"

Say, for Parameters!date.Value='1/27/15' I'd expect to see LYTD sales up to 1/31 of the respective years : 1/31/2013,1/31/2014,.. .

I was wondering if I could filter somehow on report level and yes - the expression worked for group detail. but it does not work for group total/footer.

Sum(iif(Fields!month_date.Value>DatePart(DateInterval.Month,Parameters!date.Value),0, (Fields!Prev12MonthStuff.Value))))