Dunning Letter Requires Site-Level Contact Despite Account-Level Advanced Collections Setup

I have completed the setup for Advanced Collections, with all configuration performed at the account level. At the customer account level, I have also created a contact and a profile history at the account level. The contact has the responsibility type Dunning. Everything functions correctly, and based on this setup, the strategy is correctly assigned at the account level.
However, when I attempt to send a dunning letter, I receive error messages. These errors can only be resolved by assigning a contact at the site level, which seems illogical to me given that everything else is configured at the account level.