Update!
Using the following working fine.
Rect nativeScreenExtents = tk2dCamera.Instance.NativeScreenExtents;
Rect currentScreenExtents = tk2dCamera.Instance.ScreenExtents;
However using this returns the same extents.
Rect nativeScreenExtents = Camera.allCameras[0].GetComponent<tk2dCamera>().NativeScreenExtents;
Rect currentScreenExtents = Camera.allCameras[0].GetComponent<tk2dCamera>().ScreenExtents;
Which is fine since it works. but I'm curious to why this should be the case.
Thanks.