how to configure Position Trees for routing FIN Journal Workflows ?

Hi all - We are trying to setup a THEN statement that routes the hierarchy logic based on the submitter and their placement within a custom position tree we
will maintain. ( This is needed as traditional hierarchy does not suit our current staffing mix and the business have given us the constraint of not willing to delegate and use manager/super hierarchy)

We are unsure of what the starting & Top participant should be (though we are able to select our position tree within the settings of these under hierarchy type) we are not sure if we should use get user get manager or other within that setup. and we are usure about the utilized participants all approvers selection.