AFAIK, that is set by:
Site Config > Inventory > General > Detail > Site Warehouse Defaults > Bin (Receiving)
According to this post you can update this using Receipt Entry later if is different from the above location. Beyond that you would need some sort of BPM to update the location to the Part > Site > Warehouse > Default Bin
Perhaps this would make a good idea (like many of these) to add a flag (checkbox) Default Receipt location to the above PrimBinNum.