I think that makes perfect sense if the FEH actually disengages the drivetrain. I didn't see anything in that link that would nail that down as what happens in N however, although I suspect that is the case.
I think that there is an additional issue here with respect to driver input and control over the drivetrain. I have found improved economy by pulsing up to speed, and then without lifting off the throttle, placing it into N, vs. reducing throttle.
The transition is more abrupt, but the electronics handle all of the details so that there is no revving at all, and the transition to gliding is as efficient as it can possibly be with no steady speed cruising.
Just experimenting and driving aound last evening, I was able to push my economy to 40.7 mpg after 20 minutes of driving - without holding anybody up that wasn't exceeding the speed limit.
I also found that multiple mild hills produce the highest efficiency particularly if speed can be kept under 40
mph and the ICE off on the downhills. When returning back to the flatter areas, my economy sank back into the high 30's.