TO ANY UWP DEV HERE.
If you aren't handling it in a different way,

//hide mobile status bar
if (ApiInformation.IsTypePresent("Windows.UI.ViewManagement.StatusBar"))
{
var i = StatusBar.GetForCurrentView().HideAsync();
}

this is ALL you have to friggin add to hide that hideous white space above in the app on windows 10 mobile.
Coming across too many apps which don't implement this simple thing.