Xcode button with size classes

Question

I am wanting to create a button that changes its size based on the device (Ex: 1:2 aspect ratio) in a Universal Storyboard. For example, the button would be much bigger on the iPad that it would on an iPhone. The problem I am running into is that it seems like I am unable to add the constraints needed to the button in order to make this happen. The problem is that the margins on each device are different which ends up not letting the aspect ratio solution work. Is this possible to do or I am going to have to do this separately for each device using different size classes instead of just the universal class that works for every device?