Make responsitivity more lenient to fix WP8 browser display issue

This commit should fix the issue discussed [here](http://whoaverse.com/v/whoaversedev/comments/26447) about Windows Phone 8 displaying the header incorrectly. More breathing room leniency has been added to the responsitivity values. Unfortunately, I don't know of a way to fully test the changes with the mobile browser at the moment (other than a few Firefox extensions and features), but it should be fixed.