I was doing torque training for a large military contractor. Their rule was to add 10% to the torque setting for every 2" of extension length. I questioned this so we put a wrench and a 10" extension on a transducer and digital meter and measured the results. Not even close. At a 100 ft-lbs and a stout 5" extension the wind up will be negligible. It is possible to use long spindly extensions at high settings and the torsion wind up is enough to keep the wrench from clicking. This is the theory behind torque sticks.