Essbase BSO outline formula with @AVGRANGE

Summary:

I'm trying to create a dynamic formula in the outline for the average of the last 12 months in PBCS. Account and Period are denses.

When I change to dense dimensions it works. However Year is a sparse dimension in our application and, when changed, the formula no longer works.

I've already tried use @RELXRANGE and it is not working too.

Can anyone help me make it work or is there a workaround?

Content (required):

No formulas below is working:

"Prop_Agency_Fees_Perc" = @AVGRANGE(SKIPBOTH, "Prop_Agency_Fees_Perc", @XRANGE(@MEMBER(@PREVSIBLING(@CURRMBR("Years")))->@MEMBER(@PREVSIBLING(@CURRMBR("Period"))),@MEMBER(@CURRMBR("Years"))->@MEMBER(@CURRMBR("Period")));