Can't filter out drop ships in item fulfillment search

I have a saved search returning line items on item fulfillments. We actually use this search for shipment confirmation email alerts. I have been going around this for hours and cannot find a way to filter out the line items that are drop shipped. It seems like I should be able to use the Purchase Order filter, or at least Created From fields > Purchase Order, but they do not filter out anything. When I add these as columns for results, nothing shows even when there are linked POs on the line items. I tried adding tons of other columns