AngularJs, multiple views, can a state inherit from a previous state?

Lots of the routes in my app will use an overlay with opacity to display the content. The idea is that these load up on top of the active page. I set it up like this:

<section ui-view></section>
<div class="cover" ng-class="{ 'is-open': isVisible }">
    <section ui-view="overlay"></section>
</div>

An example of an overlay state:

.state('signIn', {
    url: '/sign-in',
    views: {
        'overlay@': {
            controller: 'AuthCtrl',
            templateUrl: 'app/auth/login.html'
        }
    }
})

I have a listener in an Overlay service to detect the state changes and change the isVisible variable above. This service also restores the previous state when the overlay is closed. (I've left this out for brevity). This all works fine with one problem - the main content behind the overlay disappears!

If I set a parent state to the route; parent: 'home', then it shows the home page behind the overlay. This is perfect for when the user is on the homepage, but if they are on a different page then the homepage is shown behind the overlay not the page they were on.

Does this make sense? Does anyone have any suggestions?

Thanks!