Turns out that the iPhone 5 doesn't like the meta info.
If you take out the "width=device-width" from the meta name="viewport" part it renders in full screen.
Original:
width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
Changed to:
Note that you have to delete the icon from your home screen first and add it again after making the above change. (cache issue)
There's a nice post by Kyle Larson which goes into more detail on the above and explains how to work with startup screens on the iPhone 5.