I don't know if it helps but I ran into a similar problem, that black bar was very annoying. So as you can see at my app contactwizardpro.com I resize everything to fit the physical screen. Try it on your iPad and you will see what I mean. However it does do what you want and fit the whole screen for any resolution and zoom scale.
What I did was create a sprite variable for x and y positions. Then I hard coded the variable with the result of x or y and the app width or height accordingly. Then whenever the screen size changes I set the x and y positions to windowidth times the x variable and window height times the y variable. That resets the position according to the new window size.
If you do the exact same for sprite height and width it resizes them as well so no matter how the window resizes the layout is exactly the same as your construct2 layout.