Custom transaction fields on custom purchase order

We would like to be able to add safety stock level and reorder point as custom transaction lines on our custom purchase order transaction form. We are not able to figure out how to create the custom transaction line field and get it to show data, however,

When we configure them as type decimal number with source list item and source from safety stock level (or reorder point), they do not return any data. We assume this is due to the fact both of these fields are location specific.

Is there any way we can configure these so they will show data on our purchase order? The fields populate on the item card properly, so we assume there must be a way to get them to show on the purchase order. Creating a custom transaction line field has not been the answer.