I guess there is no way to get correct results with gl_FragCoord _ScreenParams except using “Free Aspect” in the editor’s game view?
to bump it with more info what the problem is:
The iOS views in the editor seems to use a border overlay to simulate the different screens. The result from gl_FragCoord is not related to the visible simulated screens, it is related to the whole game window including the border.
Maybe you can take the border into account by providing different shader code for the iOS version and the desktop version using these macros: