panzerwagon 

This video quite clearly shows the maths behind it. The difference arises from the fact that the shaft pivots at a different point than the fastener location. The video above uses an example of 1” apart.

As a result, manufacturers need to build a “fudge factor” into their calibration, proportional to the ratio of the handle-to-shaft-pivot distance, to the handle-to-fastener (socket) distance. If a different hand-hold is used, this fudge factor will no longer hold, and the applied torque might be very different from the torque value the wrench is set to.

I especially appreciate the closing statement in the video— “if you feel the need to convince others, do it nicely and embrace the academic debate”.