Clarification on Payroll Costing Action Types and Integration Requirements

The requirement is to develop the 'Accounting Entries to General Ledger (Third Party ERP System) . I have prepared an SQL query that retrieves accounting entries for the General Ledger report, which is attached below. However, I need clarification on a few points related to payroll costing behavior:

1. Action Type ‘P’ and Payment Costing
   Why is the action type ‘P’ (PrePayments) not included in the costing results for payments, while only the action type ‘CP’ (Costing of Payments) is considered—even though we do not have any explicit setup for costing of payments? I would like to understand the reasoning or functional background behind this behavior. (action type from the pay_payroll_actions table)