So I've been testing the ability to do a dynamic layout, automatically adjusting itself between portrait and landscape and making everything resize properly. One snag I ran into, I only have one mobile phone. I searched the forums for this and didn't find anything so, here's a resource I found that does work with C2.
You'll need a url to upload your HTML5 export to, but once you do, I can verify this tool works. I created a test project and using Screenfly, it properly reported WindowWidth and WindowHeight for every 'device' and tablet size it had listed. More importantly, my app was also able to get accurate Viewport information. As the Screenfly device size changed, the Viewport readings changed. And it continued to report accurately when the Screenfly screen was rotated (essential information if you want to keep things centered)