Well theoretically all recommended torque spec are based on the optimum stretch for the material, but as I understood it the longer a fastener, is it would need slightly more torque to be optimum.
I wouldn't think a longer fastener would always need a little more torque. I can see where the thinking comes from.
With US Standard thread form, the load on all of the threads is not even. The threads nearest the end are doing most of the work (see the mst elastic deformation). So on a really long bolt, there could be torsional twisting between the threads at the end and the toirque wrench. How much would depend on the diameter, the length, the material and the form (AN, USS, SAE etc).
Metric thread forms has the same characteristic, some argue worse.
