iOS 6 & iOS 7 Status Bar - objective-c

Question

There are multiple questions about "switching from iOS 6 Status Bar to iOS 7", but I would like to ask the opposite.
My question is: How can I make iOS 6 screen frame slip under the status bar? I tried to move the self.window.frame and self.window.bounds in App Delegate, it is okay to shift up under the status bar, but the bottom will leave a 20 ~ 40px black line.
Here is the codes:
if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 6 && [[[UIDevice currentDevice] systemVersion] floatValue] < 7) {
[application setStatusBarStyle:UIStatusBarStyleLightContent];
self.window.clipsToBounds = YES;
self.window.frame = CGRectMake(0, -20, self.window.frame.size.width, self.window.frame.size.height + 40);
self.window.bounds = CGRectMake(0, -40, self.window.frame.size.width, self.window.frame.size.height + 80);
}
I tried many values, but none fits my needs. What did I miss? I think I'm close.
Here is the mock screenshot I want to achieve ( I know the signal status of iOS 6 is not like this. Just to show the idea )
Note: only needs to support iOS 6+

Answer 1

My final solution is to remove the codes in App Delegate, and add IBOutlet to the header image of each page.
Then, in the method - (void)viewDidLayoutSubviews:
if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(#"7")) {
[iv_header setFrame:CGRectMake(0, 0, 320, 60)];
}
where the if-case is defined as:
#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v) ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)