Question on local member formula

Hi experts,

I have a simple EPM report which shows accounts in rows and datasources and entities in columns. I have selected one datasource and several entities. The datasource is a fixed selected member, the entities are select as all base level elements of a node which have a specific property value.

I now need a total column in my report. When I let EPM do it I get a formula like:

=SUM(EPMPOSITION(1), EPMPOSITION(2),...)

Such a formula is not dynamic which means I need to update the local member every time I add a new entity.

I tried this:

=SUM(EPMSELECTEDMEMBERS(ENTITY))

But that only summed the final column, not all of them.

Can anyone help me on making this formula fully dynamic?

Thanks,

Arnold