I've been getting out on the road more now and using the SG more.
I've noticed a couple things...
#1 In EV mode, since Gas consumption rate is out of the equation, it doesn't matter if you glide in N or D. Just as long as you are into some gear ( D or L ) if and when you need to come to a stop, so you can capture a bit of regen. If you can maintain no arrows on the regen screen in D, you can coast exactly the same distance as N. ( keeping the screen blank in D can be a challenge though... in that regard... N can be an advantage...)
#2 If you need to glide with the ICE on... ( because your speed is over 40, or it's too cold for example... ) It looks BETTER to glide in DRIVE. Watching the SG and the NAV display... they BOTH DROP in MPG when coasting in N. This seems backwards, but it was consistant over 15 miles and 45 Minutes of P&G. This is for sure better for the NUMBERS on the screen. Real life... TBD....
"Coasting" in D ( no gas pedal ) from 35MPH to 25MPH with engine on = 95 to 75 MPG.
"Coasting" in N, with engine on from 35MPH to 25MPH = 55 to 35 MPG.
( on my particular road, your results may varry... hopefully, the proportion is the same...)
I'm having a hard time describing why this is... because I know you can coast the same distance no matter if you are in N or D as long as you keep regen or engine braking out of the equation.
I have a theory though... it's probably an instrument problem.
Since the SG is not measureing the actaul amount of liquid fuel going into the engine... it has to INFER what's being used from other conditions.
In N, perhaps the RPM's go up a tad, since there is no load?
In N, perhaps a bit more mass of air flow is detected?
Most likely, something is going on in N that "tricks" some sensors.
Gary, this would help explain why your SG reads lower than actual.
You sound like you spend a lot of time in N. N on mine tricks the SG to read low... and by a significant amount. I'm talking engine on time. There is no such effect in EV.
How many actual gallons and actual miles have you done since having the Scangauge?
I'm still on my first tank... takes a while to empty that sucker when you're getting 40+ MPG! And this is that monster 18 gallon fill up. When I do need to get gas, I'm going to do the usual "3-clicks" at the pump... then I'll add 3 gallons to that number, since I forced nearly 100% of the air out last time.
I think you and I can for sure tell the difference between a 40MPG tank, and a 45MPG tank... but I don't think you can measure the difference ( at the pump ) between 44 and 45MPG. There is AT LEAST 1 MPG of "play" each time you fill up. This time, I may have to put +/- 2 MPG in the notes section of the database... since I'm not going to spend 20 minutes trying to shove 18 gallons in there next time. I was hoping something like the SG would be more reliable than the human pumper... but I think not. I've gone 129 miles this tank, and MTE = 475 now. And this is in below freezing temperatures. This puts me at 35MPG if the car has figured out I added 18 gallons... and at 42 MPG if it still bases it on 15.
The Nav display is at 38.x MPG right now... ironically, right in the middle!
Gary, where's your real mileage database on GH????
P.S. I'm glad you agree driving with the key off is a bad idea, and that was a 1 day event.

I'd be more than happy to drop the subject now... so long as you're not promoting this as something people should do.