Where/What table is the Participant in Manage Project Change Order?

Summary: We are currently Implementing the Manage Project Change Order and currently testing the Approval workflow and I see that the Participant box is not showing all the Employees on the list. Is the participant box pulling specifically for the Resource Pool? How will we change it and make sure all the HCM Employees will pulled on the LOV?

Content (please ensure you mask any confidential information): Checking on what/where table pulling the Participant in the Manage Project Change Order, Not all Employee is pulled on the LOV. is there any requirement to pull or specific resources only will be included on the Participant.