The spec already states you get up to 10 hours of usage.

> Up to 10 hours of surfing the web on Wi-Fi, watching video, or listening to music
> Up to 9 hours of surfing the web using cellular data network

So, if you're getting that based on your observation, I don't see why this is an issue. Up to means whatever lowest possible settings you have set for your usage. So, imagine if every other settings are turned on with all notifications enabled. You will get lesser amount of usage time from a fully charged device.