from the factory, bob long guns come pre set at a certain pressure (i forget what this is for the victory) and the guns perform very well at that pressure.
sweet spotting (from what i understand) is where you find the lowest possible lpr and hpr pressures to shoot 285fps. Usually the factory pressures do a very good job at this.
the problem with having two regulators is sometimes people screw things up. the victory can run 65psi lpr just fine in factory form. What happens when you put the hpr to 280psi (stock is less than 200psi i think) Too high of an hpr pressure will require the lpr pressure to be increased in order to hit the valve open hard enough (because the hpr pressure aides in holding the poppet valve closed) More pressure is required to open a valve that has more pressure holding it shut. The result, a kicky loud inefficient gun.
basically you might shoot 285 fps at 70lpr, 190hpr but you might also shoot 285fps at 90lpr, 250hpr. The goal is to get both the lowest you possibly can. To make this easy, bob long has pressure testing tools that tell you both of your pressures, you just set them to the factory recommended pressure and call it a day.
the blue is hpr air, and the green is lpr air. you can see how it is a balancing act.