Samsung wants to answer "yes" to every possible tablet size need, Samsung chief strategy officer Omar Khan said. What are the guidelines (or general practice)

Samsung wants to answer "yes" to every possible tablet size need, Samsung chief strategy officer Omar Khan said. What are the guidelines (or general practice) for creating apps that scale across so many sizes? My understanding is that Android apps tend to scale well across minor screen size/pixel density/aspect ratio variations, which is good, but I also note that most universal iOS apps have substantially different layouts between their iPhone and iPad versions: not just differing sizes but a very different arrangement of controls and even substantially differing functionality and interaction paradigms... for example, iPhone apps tend to be much more about drilling down into a hierarchy while iPad apps are "flatter". Is there a guideline regarding where to make that cutoff? In a world of 3.5" and 9.7" screens being the only two options, it's easy to know which device gets the "little" layout and which gets the "big" one... but what sort of layouts should an app give 5", 7", and 12" tablets?