In general, the power allowed on any of the 2.4GHz channels is the same, so the range is the same. However, some regulatory agencies have strict rules about out-of-band emissions on the edge of the band, and if a manufacturer was having a problem getting their radio to pass the out-of-band emissions test at one edge of the band or the other, they may have chosen to work around the problem by decreasing their transmit power on band-edge channels (1 and 11, or 1 and 13) to get below the failure threshold.
So, without actually carefully measuring the power output of your box using radio laboratory equipment, it's hard to say, but channel 6 might be a better choice on some boxes rather than a band-edge channel.