That is a very good question, and shows rare perception.
Although Volvo resistance wires may vary by only four inches, on domestic V-8 engines the variation may be as much as 10 or 12 inches. What is important is that a threshold resistance is achieved that results in an adequate firing voltage for the shortest plug wire. Beyond that length given good primary performance, the firing voltage is essentially similar. It is helpful to observe an old time ignition oscilloscope in action to see the effect of increasing resistance.
In the sixties Bosch used copper core wires, and used a pellet resistor in the plug connector, and sometimes another in the distributor cap connector, to ensure equal resistance on all plugs leads.