Thomas, you mentioned the "sweet spot" is where there is metal all the way down, this leads me to believe that the cross section directly under the work is the most important, and I can only think of one reason. Perhaps with increased depth there is more cross sectional area under the perimeter the piece, which would decrease the shear stress on the anvil steel which would decrease deformation in the anvil, allowing more on the energy from the blow to go into the work-piece (Like even though it's just elastic deformation, I feel like by the time the anvil steel releases that energy the hammer blow is already over, so it's basically useless). Does this sound sorta right, or is there another explanation? I think I'll also ask one of my professors what he thinks next week.