The wrench is calibrated from the handle to the socket lug for whatever length that is and torque applied will vary if you put a tool (such as a crow foot or a barrel wrench) on the end that extends out past the socket lug. Think of it this way, if you put a pipe cheater on the handle and made the wrench 2' longer, you'd expect the torque to be different than the scale right?

Here is a handy calculator to help figure the value...
http://www.belknaptools.com/support-...ns-calculator/