In-Class status bar along with Navigation controller

I have application designed for the iOS 8 and above. The app has UINavigationBar and contents are drawn programmatically using navigation bar height as reference.

When a call is received, the status bar height will get changed and appears with the in-call message.

Scenario 1: For portrait mode the navigation bar appears below the status bar and the calculation for status and navigation bar height are as below.

enter image description here

Status bar : 40px
Navigation bar: 44px

Scenario 2: When the device is rotated to portrait mode upside down, the status bar overlaps on the navigation bar and calculations results the same as above.

Using the UIApplicationWillChangeStatusBarFrameNotification to check the status bar height.

enter image description here

Is this is expected behaviour and way to check that the status bar is overlapped on navigation bar in scenario #2.

Please suggest.