6 is way too high. The Ford spec is 1.05 to 1.15 ohms.
Think of the ignition coil like a tank you are filling with electricity. When the module first grounds the coil and the coil starts filling up with energy, to the circuit and the module it looks like a dead short for a instant. The small resistance in the circuit throttles the amount of current that is able to pass through the circuit, and the module is part of this circuit. As the coil fills up, the amount of current is less and less.
That is why the module tends to fail without the resistor, there is too much current going through it. 1 ohm is not much resistance, but it is enough to drop the voltage across the coil from 12 down to 9-10v when the engine is running.
The Ford TFI and the GM HEI both have current limiting circuits built into the module, so they do not need external resistance.