VA Outline always navigates inside current file, whether it is .cpp file or header file with just header of the function (method). We could use more control over this process, by the use of right-click menu item, for example.
Yes, VA Outline was designed to navigate in current file. But after you jumped to a location, you can use Alt+G over the method name and VAX will jump to the method in the corresponding (cpp/h) file. Also you can use Alt+O to switch between source and header files before you start to browse the file, so you will see the list which you need.
Yes, this makes it click+shortcut key action. Why not support Alt+G in VA Outline itself to actually go to implementation as an alternative to default Goto?