How not to calculate the Self Assessed Tax at Supplier

Hello Experts,

we have an issue with Self Assessed Tax. We have a supplier who we are using to pay for both Oracle Projects and non-Project related invoices. The supplier is setup with Calculate Sales Tax as well as Self Assessed Tax at the supplier level.

Our Projects related PO's includes Sales Tax amount. Hence we didn't want to calculate the Sales Tax and to achieve this, we have created a separate site (and location) for the supplier and have set the Calculate Tax to "No". However, we don't want to calculate the Self Assessed Tax at invoice side as well, with out disturbing the set up at the header level.