Find event to set Billing type after demand import

We would like to set off a BPM or some process to auto populate the billing type field in the Order Head Manifest Billing area for EDI orders. OrderHed.PayFlag
It works if we create a new order manually, as its set on the change ShipTo event, but not when coming from EDI. I am *thinking it has something to do with the order being created in demand tables first, where that field isn’t available.
Can anyone help find what event I would set this at? I would only want this to run once at the beginning of an order.

I tried to set trace flags and then trace what happens when I import an edi file, but did not have any luck.

Have you tried setting the default on the customer/shipTo master.

Yes, that is set and does not carry over when the order is from EDI.