There is both a component and helper that help to work around some URL issues.
If you need to merge in defaults to your URLs, you can get the information from the defaults() method:
// From inside a plugin controller
$$this->redirect(['controller' => 'Main', 'action' => 'index'] + $this->Url->defaults());
It will basically add in 'prefix' => false, 'plugin' => false.
You can in that case also just use the convenience method:
$url = $this->Url->reset(['controller' => 'Main', 'action' => 'overview']);
Inside /admin/plugin-name/example/action the URL to redirect to would normally become /admin/plugin-name/main/overview.
With the reset() method it will become the desired: /main/overview.
In both cases, however, the query strings are not passed on. If you want that, you can use the other convenience method:
$url = $this->Url->complete(['controller' => 'Main', 'action' => 'overview']);
Now if there was a query string ?q=x on the current action, it would also be passed along as /main/overview?q=x.
For generating links for those cases please see Html helper.