If the 40 ft-lb spec called for a particular length crowfoot run parallel on a particular length torque wrench, then that would be correct. However The crowfoot is usually run at exactly 90 degrees to avoid extra leverage.
The formula to calculate what to set the torque wrench to follows (example is 18.5” torque wrench, 3” adapter):
Torque Wrench Length X Torque Desired) = (18.5 x 40) = 740
Divided by:
(Torque Wrench Length + Extension Length) = (18.5 + 3) = 21.5 inches
740 / 21.5 = 34.42 ft.-lbs.
That’s 16% in this example. Most automotive fasteners expect a 10% variation, maybe firearms are more tolerant.