2lis_02_itm - Why wont the PO extract?

Hello,

I am trying to find out what the rules are for the 2lis_02_item extractor.

Just running some tests in RSA3 with a full extract.

Some purchase orders are extracted using this extractor, others produce no records during the extract test.

I am trying to work out what might be causing the difference. Looking at the EKKO table, I am struggling to see what fields the extractor is checking. I thought it might be looking at the FRGKE field or the FRGZU field. But I have examples I can see where both PO's have the same value on EKKO, and one PO is extracted, and the other isnt.

How can I find out what logic the code is using to decide here?

Thanks.