They look like they fire like you said, but they don't.
The 3 coils are in a line, but inside the potting they have straps or wires directing the spark to the appropriate cylinders.
The 4.0 firing order is 153624 (15 too young, 36 too old, 24 just right.)
They fire in pairs - each coil fires 2 cylinders at a time - in each firing one fires a cylinder under compression on the firing stroke, the other cylinder fires after the exhaust valve closed and before the intake opens. That's called the waste spark.
They fire complimentary or companion cylinders together:
1 and 6
5 and 2
3 and 4
A good way I've found to find a bad coil rail - LISTEN carefully. If you hear it sparking it's shorting inside.
Another good way - rev it for about one minute - go underneath while it's running - use a laser thermometer right on the exhaust outlets. If the rail is breaking down one cylinder will be colder than the others, and the complimentary (companion) cylinder will be too hot.
The last resort - swap it out.
Too bad there's no fixing them.
Be sure to get high quality coil rails. Autozone and the like sell a Chinese knock-off, it may last a few months. Dealers, NAPA, Car Quest sell better quality - made by Standard Ignition. They cost a little more but are well worth it!