okay, I'm talking out my
right now, but I THINK...
with 4 cylinders, #1 and #4 fire 180* apart and #2 and #3 fire 180* apart. So you can spark #1 and #4 simultaneously at 180* and it'll hit each cylinder twice in its four strokes, but the extra one falls at the end of the exhaust stroke and is basically wasted. Seems like a waste, but you can then run 4 cylinders on two coils by firing them twice as often.
That's my thought on it. I'm sure others know better, or at least know the right terminology
A