I have found different characteristic values given for the standoff distance to achieve optimal jet formation and therefore penetration using a shaped charge. Walter and Zukas give 2-4 cone diameters. Another plot I saw peaked at 60 cm for a 10 cm CD and the acceptable range was 2-6 CD. Is there an equation to determine the optimum theoretical standoff distance for a shaped charge? I suspect such an equation would take into account the cone liner material, density, mass ratio to explosive material to liner, liner thickness, etc. What is the optimum standoff distance for a shaped charge to achieve maximum penetration?