What tax setup is required to use the Merchant Reference field on Expense Report to determine tax

This applies to 24C

I enabled Expense Location and Merchant Reference tax fields on Expense Reports. I cannot find the Merchant Reference field when defining Determining Factor Sets. What tax setup is required to enable Merchant Reference to be used in Tax Rules? Examples of our existing tax setup is shown below

Here is an example of our existing tax setup:

VAT Jurisdiction:

Business Unit Tax Profiles:

VAT Rate to be used with Merchant Reference