OK, so if these are the same numbers for both customer and item tax statuses, then if a customer has a status of 3 (tax exempt) on an invoice then no tax should be calculated. Regardless of the item tax statuses.
If the customer tax status is anything other than 3, then there will be tax determined for all items other than those that are tax exempt themselves.
A customer with status 2 and an item with status 1 will get a 6% tax charged for that item, as it's the lower rate. A customer with status 2 and an item with status 3 will have 0% tax charged for that item, as 0 is the lower rate. Essentially, tax is s total of all of these combinations of customer and item rate comparisons.
Hopefully this helps in making updates to your tax table in order to be charging the intended tax to your customers on invoices.
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Regards,
Softrak Tech Support