As long as your editable text webpart is on your parent page template and you have the subpage placeholder on that parent page template, this should work. I set the webpart to have default text of {% CurrentDocument.DocumentName |(identity)GlobalAdministrator%}
in the properties, not in the actual Page content. I don't have "inherit content if empty" checked. And it shows on sub pages. I have a structure of:
/About
/About/History
/About/Organization
And on the History and Organization pages, it displays "About" above the navigation. Very similar structure/format as you have.