The supporting multiple screen sizes tutorial is a complete waste of time for mobile devices.
As far as I can tell, very few people are using C2 for mobile HTML5
After a month of groping in the dark and trying many different options, we took this approach:
1) use crop full screen mode.
2) make the backgroud 1024x1024 and center it.
3) make the screen size iphone 4 resolution = 640x832 and 960x536
3.5) use anchors to glue HUD bars, buttons etc to the corners/edges so they expand out to fill available space on longer thinner devices.
4) every tick examine the screen width/height and see if its changed.
5) if the size has changed, scale all layers except background to best fit keeping aspect ratio
6) Hack the index.html to make the browsers address bar go away in iphone and android
7) Export a version of the project with retina display switched off for the ipad 3. (have to detect in in js). ipad 3 will scale up ipad one resolution, which is 1024x768 - tool bars etc. you wont be able to tell the difference.
8) have separate layouts for portrait and landscape modes, and you have to store the state of your game as when you switch layouts, it destoys everthing.
9) Export a version for the PC with fixed size or letter box scaling and landscape mode.
10) had problems getting anything to work properly on iphone3 - decided not to support it (the only way to detect it is to run a speed test in js).
11) C2 has no concept of modal dialogues, and no way to disable users clicking on sprites, even if they are invisible and hiden under layers/bottom of z-depth. you have to design your game with all the user input in a small a number of groups as possible, and then disable groups to switch of game input while diplaying psudo-dialogs.
12) dont forget to select the option in the touch settings to make mouse input act as touch.
I implemented swipe also, to swipe in left and right layouts with settings, info etc. There is no gesture support, so I wrote my own just tracking the touch coordinates.