         }
         
         let dataSource: OBShutterTransitionDelegateBehaviorDataSource? = getDataSource()
-        let height = dataSource?.topHeight ?? .defaultTopHeight
+        let height = dataSource?.topHeight ?? shutterHeight
         
         (topView, bottomView) = split(view: presentedView, at: height)
         

// the two views offscreen. The transition animates the top and bottom views
// coming together, as they combine to create the presented view
public final class OBShutterTransitionDelegateBehavior: OBTransitionDelegateBehavior {
    private var topView: UIImageView?
    private var bottomView: UIImageView?
    private var subviews: [UIView]?

        }
        
        let dataSource: OBShutterTransitionDelegateBehaviorDataSource? = getDataSource()
        let height = dataSource?.topHeight ?? shutterHeight
        
        let (topView, bottomView) = split(view: presentingView, at: height)
        
