How can I make the Tax Rules use supplier site country

Morning

We are a UK based business. We have a few suppliers where the country of origin is outside of the UK, however they have branches in the UK with UK VAT numbers. When our tax is calculated for these supplier invoices, the country of origin that is used is the main address of the supplier so all of the tax is calculated as reverse charge. How can I get the rules to use the country at site level so that the tax is calculated correctly.

Also in the FTR the country of origin for all sites is showing as the main country of the supplier and not the site - so it is flagged at audit that the tax code has been manually changed on the invoice workbench.