ops, it looks like that the preference panel for the 13" display is structured differently (less UI elements with a different hierarchy, I guess)
not having a 13" myself, it's kinda hard for me to fix it. The best thing I can do is suggest you to download Accessibility Inspector (it comes with Xcode, see here https://developer.apple.com/library/mac/documentation/Accessibility/Conceptual/AccessibilityMacOSX/OSXAXTesting/OSXAXTestingApps.html for description on how to use it) to figure out the hierarchy of the UI.