Thanks!
Well I probably picked a poor resolution to use for iOS because it doesn't quite scale properly using Ejecta, so I had to fake it by making the background black. Using Cocoonjs's 'Stretch to Fill' option works perfectly though (using it for Android).
For both web and mobile my screen resolution is 640x960 (4th gen iPod even though I was using a 5th gen for dev). My fullscreen in browser setting is 'Letterbox Scale', and 'Unbounded scrolling' is set to 'Yes'.