Another thing that I can think of that could disturb the mini J cabin from Y is on red-eyes where the main meal services are at different times for each cabin. For example, on the 10-ish pm departure from BKK, dinner is served in the Y cabin, but breakfast is served right before arrival in J. That is to say, if you’re a light sleeper and trying to get some shut-eye immediately on a red-eye you might have trouble falling asleep while the light is on in Y with passengers eating.

Of course, this can be easily preempted by pregaming appropriately in the lounge and/or asking for some Japanese whiskey right after takeoff.