It is still the same answer as explained above.
the payment terms that are used in the PO process are stored in the purchasing data view in a vendor master, and this is purchasing org specific, and the only breakdown that you can add is the plant level.
a purchasing organisation is a element in the enterprise structure, it is a reporting level, and it makes the most sense if it matches with the organisational structure that is lived in your company.
Just creating a new Purchasing Org to separate company specific payment terms is not a logical way from my point of view. however, I cannot really believe that a central purchasing organization (if you have just one - what I assume because of your question) negotiates company specific different payment terms with one vendor. Such things sound like negotiations are conducted by different physical organizations and your enterprise structure is not setup like this.