filtering repeat region that contains relations

[wildmodeler]

I am trying to filter a repeat region (RR) that has relations running to create the find number (FN). Here is what I have:
We use a completely parametric bom in our drawings. Each part/assembly has a parameter FN & PL_SORT that we use to sort the RR. Here is my problem. One of our other groups is using a "library" where the parts do not have these parameters. Since they are locked "library" files I cant add the required parameters. To get around this I have written a relation calling the part name and making the fn with the relation.
Relation:
if asm_mbr_name == "FW1_4B"
fn = "199"
else
fn = asm_mbr_fn
endif

Where the table column has "&rpt.rel.fn" Running the column. It works and changes the callout to the correct FN number.
The problem is with the sort.
I use this to sort:
&asm.mbr.pl_sort Forward
&rpt.rel.fn Forward
&asm.mbr.fn Forward

The part run by the relation comes out last on the bom no matter what.
If this makes any sense give me some ideas of how to sort it.
Thanks