eski You may want to try:
1. 16:9, Scale Inner scaling, set window size to 1600x900(landscape), make sure to keep a border of space where you want elements to appear on smaller screens
2. 16:9, Scale Outer (I think), set window size to 800x400(landscape), set your layout size to 1280x1024 (this works like a dream for me, at least for PC and on Android for both tablets + phones!) See the CocoonJS Plugin Demo Capx for this solution.
Flip resolutions for portrait. Good luck!