@Prad Likely because without the amplitude or freq. It can't move nearly at all.
By its speed and lifetime, its range would be 0. Amp. and Freq. artificially creates the range for the weapon.
Its some combination of the arc gap, shots, and frequency/amp. The game nor the calculator calculates this as the range, despite working as range.
Its 'real' range is around 3.3 - 3.5, in case you're wondering. [At least for this example.]