I think it’d be helpful to be able to adjust the screen size some in the live preview. OR at least have more clarity on how “big” the screen is in the live test view. Initial impression when I run a live preview is that it’s a very tiny phone, like an old iPhone 4/5 size. Knowing what the assumed resolution of that screen is would be helpful when setting the sizes of objects and fonts and such.
Apparently Apple forces them to have the white bar there in test mode, so not much can be done about that. You wont really know how it will look until you download the app to iOS.
The best way to set up the screen is using layouts, as it keep things in proportions. So headers and footers have exact pixel measurements, but the middle contents can be set to “stretch” mode which will resize depending on size of the screen.
Here’s an example:
