When there are several approvers within the same office, there will not be any system to which of these users get the invoice for approval when the invoice is sent to that office. If the hierarchy was set up like this, then that will be the default behaviour. Any one of them could get the invoice for approval. See image below, where all the users marked in red are approvers:
However, you may set up a default approver for that office; an "office approver". So that unless the acceptor specifies an approver themselves, the invoice will automatically go to this approver when it arrives to that office.
How to set it up
From the main menu, click "offices and users":
Select the office where you would like to assign the office approver, and click the "details" tab. In the drop-down box, you will see all the approvers within the office. Select the person that you would like to make the default office approver, and click "save".
Note: The approval of the office approver does not hold any more "weight" or authority than any other approver, when all other things are equal. Having an office approver merely means that invoices will be routed to this person by default.