Customer Contract: Restrict Primary Party visibility

Summary:
How do I restrict the customers that are visible in the Primary Party search when creating a customer contract?

Content (please ensure you mask any confidential information):

I'm doing an implementation of CX Sales and Sales Contract. For CX Sales, I have customized the Salesperson job role to restrict the account (customer) visibility, and also use Sales Territories and Access Group mechanism to supplement account security.

However, the same sales user can still see all customers in the Primary Party search when creating a Customer Contract. The account security in CX Sales does not take effect on the Customer Contract.