R03B551 - Batch receipts processing - not populating Minor write-off account when running R03B551

We are using F03B13Z1 to populate the data for a receipt to be applied to the customers account. The tolerance is set to 5.00. A receipt is processes for $4000, the invoice it is being applied to is for 4000.50. We have set the processing options to produce a minor write off for the .50. The data is correctly being written to the F03B13 and the F03B14 but the minor write-off account associated with the MW code is not being populated. When we then try to post the batch it errors out as this field cannot be blank.

I had assumed it would use the AAI RAMW to return the minor write-off account, which it isn't doing. If I manually process the receipt through standard receipt processing, it populates this field and posts successfully. What am I missing?