Hi, could someone clarify for me how the autobrightness should work on the 5s? With my iPad and iPhone 4s, if I switch off autobrightness, the brightness shoots up. With the 5s, it doesn't change at all. Instead, when it is turned on the actual setting seems to creep up and down. It also seems to be quite bright in low settings and not quite bright enough in light but I've read some people say you can calibrate it. It definitely seems different to my other iOS devices but when I saw the scrubber creep up an down I felt a bit relieved. Is this normal for 5 and 5s?