I have a subdirectory in my controllers folder - possibly to set default controller?

Hm. It would seem that a default controller in a subdirectory cannot have methods other than index?

For example, I have a subdirectory with a default controller in it:

PHP Code:

// application/controllers/subdir/Welcome.php
defined('BASEPATH') OR exit('No direct script access allowed');

class Welcome extends MY_Controller {
     public function _remap($method) {
        echo "calling " . __METHOD__ . " with \$method=" . $method;
     }
} // class subdir/Welcome 


My intuition says that this _remap function should kick in when any method in the subdir folder is called:
http://example.com/subdir
http://example.com/subdir/foo
http://example.com/subdir/bar

However, I get 404/not found for both the foo and bar urls. I am forced to define other controller classes to get those urls served.

Is this supposed to be the case? Is there no way to define a default controller in a subdirectory that handles *all* requests for that subdir?