Calculating Row Total dinamically

Hi experts!

I want to create a total on rows in my report.

If I use one dimension on rows, my grand total works fine ( I have create a excel formula; SUM of my range that I want to sum) and automatically EPM create a local member called total with this formula:  =SUM(EPMSELECTEDMEMBERS(PRODFAMILY))

My problem is if I have two dimensions on rows, If I do same formula my local member isn't dinamic and I can see this formula: =SUM(EPMPOSITION(1), EPMPOSITION(2), EPMPOSITION(3), EPMPOSITION(4), EPMPOSITION(5), EPMPOSITION(6))

In my first report doesn't matter number of rows and works fine, in my second doesn't work.

Any help?

Thanks!!