Extending OAF Entity Object/JDeveloper Defaulting Question

I am looking to extend the OAF Customer Account Site Details region via customer standard in Oracle Apps 12.1.3.  I would like to default a DFF on the customer accounts site record from data in another site record on ‘Insert (new)’, defaulting data from a ‘bill to’ record to a ‘ship-to’ record based on the customer account.  My thought was to do an Entity Object extension via JDeveloper.

Does anyone know how to utilize the ‘Query Column/Expression’ in Step 3 (Pic below)?  Not finding any documentation on it?  Is this a regular query/select or other?  I am open to other ways of implementing this logic if I am going down the wrong path.