the "missing" sir cumference is more likely the distance from center of wrench contact on the flats to same point on opposite flat. That's the effective circumference over which you apply the torque with the wrench alone (and thus the wrench reading). You have to pull the wrench harder to torque a large fastener to 50ftlbs than you do a smaller nut, because your mechanical advantage is less. Now how did I screw up the logic on that one....

Not responsible for advice not taken...