The iPhone 5 tries to make its signal bar and reception look better than it really is. Do you Want to know what your reception actually is? You need to use the Engineering mode. Type *3001#12345#* into the dialler and hit the call button and you’ll enter Field Test mode. This changes the bar-based signal indicator to a “proper” numerical figure. There are also menus to tell you all sorts of other signal information, however many are lost on how this works.