1. I think you may have to go for custom report as SAP standard and IRS requirement is to report by TIN.
2. Run Report only by One Co code in report parameter. (Legally you have to report only for one co code in 1 FIRE File)
3. Change Configuration of Variant Withholding Tax Itesm as following. It will show all cleared item of each unique vendor no. Therefore you will get two seperate group of cleared items for vendor A and Vendor B even if they have same TIN.
All the best.
