How to properly position the back button in iOS7

EDIT
I think I might have found the trick (in iOS 7 Design Resource — UIKit User Interface Catalog.)
Under Bar Button Items

Note that a bar button image will be automatically rendered as a template image within a navigation bar, unless you explicitly set its rendering mode to UIImageRenderingModeAlwaysOriginal. For more information, see Template Images.

Under Template Images they have some code to specify the UIImageRenderingMode.

UIImage *myImage = [UIImage imageNamed:@"back"];
UIImage *backButtonImage = [myImage imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];  
// now use the new backButtomImage
[[UINavigationBar appearance] setBackIndicatorImage:backButtonImage];
[[UINavigationBar appearance] setBackIndicatorTransitionMaskImage:backButtonImage];

Try creating the UIImage with alignment insets and then set the Back Indicator image.

UIEdgeInsets insets = UIEdgeInsetsMake(10, 0, 0, 0); // or (0, 0, -10.0, 0)
UIImage *alignedImage = [[UIImage imageNamed:@"back"] imageWithAlignmentRectInsets:insets];  
[[UINavigationBar appearance] setBackIndicatorImage:alignedImage];
[[UINavigationBar appearance] setBackIndicatorTransitionMaskImage:alignedImage];

You might also try adjusting the position of the UINavigationBar title text

[[UINavigationBar appearance] setTitleVerticalPositionAdjustment:(CGFloat)adjustment forBarMetrics:(UIBarMetrics)barMetrics];