If the rotor is rightly phased it will move about one half it's travel range from before to a half-range after the tower. The electrons will jump from anywhere on that rotor, to the nearest conductive surface with the lowest resistance; including constructing it's own conductors namely carbon tracks. That rotor half-range has to be less than half the distance between the towers, or the spark could still jump to the wrong tower, on account of it's not real happy to jump the spark plug in the first place , in the cylinder under pressure. If it takes 20,000 volts to jump the proper one and 5000 to jump the previous one, which is now on the power stroke, or 5000 on the next one now on the intake stroke; guess which one it's going to fire.
If the phasing is off by too much, it is possible for the spark , which in most systems can jump even a 1/2" gap in open air, to jump to the wrong tower.
On a D from a slanty or an old 318 where there might be 30* or more of mechanical advance in the cam, I have occasionally had to file the rotor-tip at a severe angle to ensure reliable arcing to the correct tower. That 30*on the damper is 15 inside the D and there is only 45* between towers and half of that is 22.5. So, with 5* idle timing, and really crappy phasing, it is theoretically possible to be pushing the envelope, as the mechanical advance finishes up, giving your engine fits at somewhere after 3000rpm on a stocker.
I guess it doesn't happen often cuz in 50 years I've only run into it a few times, and I was not an auto mechanic all those years,lol. The longest I ever held one job was 5.5 years, altho I went back to one same employer three times; you know; money talks.
