Behavior of using Office Web Apps Server 2013 and SharePoint 2013 with multiple zones
Configuration of Office Web App Server with multiple alternate access mappings and zones in SharePoint Server 2013.
Office Web App Server 2013 will use the default zone set in SharePoint Server 2013 for the respective web application.
The default zone URL is http://sp2013t ,so this is the URL that Office Web Apps will use to contact the SharePoint Server.
You can test and make sure the URL is accessible from the Office Web Apps server, if it is not you will need to correct the connectivity here or Office Web Apps will not work correctly.