Oh, i forgot to mention that for a tanto knife, the WEPS will sharpen the long edge as a perfect dihedral (in theory). And if you upgrade the WEPS with the Pro-Pack II so that it uses spherical joints, then it can sharpen both the main edge and the tip as a perfect dihedral (in theory). Details about this can be found in the chapter about the WEPS and also the chapter on optimal pivot placement.
The EP can sharpen a perfect dihedral angle, if you are sharpening at 30 degrees per side on the Edge Pro Apex, and 15 degrees per side for the Edge Pro Professional. Details about this are in the chapter about the Edge Pro Apex.
The chapter about the Edge Pro Apex also talks about modifications to the designs that would make them perfect in theory.