I'm building a share extension for my iOS app and I can't use the default `SLComposeServiceViewController`, so I created (in the storyboard) a basic `UIViewController` and embedded in a navigation controller. I get to present it, dismiss it etc but it's always full screen. I would like to make it look more like a dialog. 
I have tried using `self.preferredContentSize` on my view controller, tried `Use Preferred Explicit Size` on the navigation controller in Interface Builder, but it doesn't work.