The first place it should come from is the Default Location on the Inventory Part.
If the Inventory Part doesn’t have a default location defined, then it will be a somewhat random selection of previous inventory locations that the item has been stored in. You can the choices by looking at Count Per Inventory Part and review all of the locations that have been used for the part. If you don’t want any to appear AND their current Quantity on Hand is zero, you can delete the record from this view. Best practice is to define a default location for every inventory part, this provides the most consistent Proposed Location.
It first looks at the work center or production line outbound location for the last operation, then the inventory part default location. Previous inventory locations should not affect how the proposed location is fetched.