Requisition Attachment (header level) in Purchase Order line

I don't understand why requisition header level attachment are getting duplicated for each purchase order line.  I know it's not a bug but a feature but why would i want the physical copie of the file getting duplicated X times ?  Our current use case is that we have 1 bill with every items we purchased on it.  We then make a requistion, each requisition line correspond to an item on the bill.  Then we attach the bill to the requistion header.  Then bill then get duplicated for each single line in the requisition. 

Is there a way to only have the logical reference in FND_DOCUMENTS to be duplicated and not the physical part in FND_LOBS ?  Or is there a way to have that bill attachment only duplicated one time to the purchase order ?