Is the "Total Average" MPG legit?

That's probably closest to being correct as far as OVERALL mpg, EV + HV. Looks like your doing a lot of ICE driving. Mine is around 115, because my commute is a few miles beyond my EV range. My ICE usually fires, warms up, then shuts down at the light, as I enter the parking lot to my facility. If it's still running when I park, I'll let the engine complete it's warming cycle before shutting down. You'll know when the warm-up cycle is complete because the car is stationary and in park. The ECU won't shut-down the ICE until the warming cycle is complete. Once the ICE stops, it's OK to shut-down the car.
I don't think the car's ECU segregates EV vs ICE operations in their calculations, otherwise Toyota would be able to tell you when you need an oil change (like the GM products) rather than trip a alert every 5K. I know the gen4 can't do that and I doubt they've improved that on the gen5.
The only way I can track actual ICE is by the miles on a tankful of gas driven, divided by the miles driven. Then use EV/ICE percentage to calculate how much is EV vs ICE. That's about as close as you can get.

Hope this helps...

 

The Total Average MPG is a totally worthless value to me. Toyota doesn’t break out Miles on gas from miles on battery, so I keep track myself. It is a pain, but I want to know how many miles I get on a gallon of gas (46 MPG) and how many miles per kWh bought from the wall (3.35 mi/kWh or an average 42 miles for a 12.7kWh charge at 120volts)

 

For short trips, average fuel consumption will never be fair.
When you drive long distances, the magic of large savings numbers works))

 

I can't speak specifically to the Prius Prime, but for my RAV4 Prime, it is far too high to be HV-mode only. I've been assuming it is total miles (EV+HV) / total gallons, as it seems in the ballpark for that. Though haven't used this setting much.

At 9600 miles, it is currently showing me a total MPG of 56.9, which far exceeds anything what it really achieves. I'm taking that to mean that it has driven very roughly about 2/3rds of its miles on gas, 1/3rd in EV.

Between how it automatically goes into EV mode on downhills even when I have set HV mode, combined with how I often use HV for uphill and EV for downhill (including shallow slopes where it won't automatically go into EV), any such separation isn't going to make it comparable to how my former Prius expressed (HV) MPG. Both of this two behaviors (one of the car itself, the other my use of it), would tend to artificially shrink HV-MPG and inflate EV-miles/kWh.

 

Yep; whenever I'm in the mountains I get 25+miles/KwH - you can't tell me that's accurate; considering I went up that same mountain earlier that day.

 

Descending mountains after a hike, I often see 99.9 miles/kWh, along with an increased EV range. I.e. regenerative braking has increased battery charge. But these readings apply to this trip only, since restarting car.

After the road slope diminishes to the point the car won't glide anymore, or at least not fast enough to blend in with traffic, and the EV ranges drops to less than it had at restart, the miles/kWh plummets rapidly to single digits, then slowly to something reasonable or until EV range vanishes and it switches to HV.

 

According to the Prius display table, it's a daily average, not a start-up trip average. That's the problem I have with it - if it's a trip average, there should be a tally on every startup. The 25+miles/KwH only makes sense if it was the trip down the mountain ONLY, not a daily tally as indicated by the OEM table.

 

I haven't (at least yet) found such a choice in my RAV4, despite seeming to remember something similar somewhere in Owner's Manual. There is much I haven't yet absorbed or learned. The menu I've been using gives only two choices, single trip or overall, not daily or Trip A/B.

 

You may not have that table, if it isn't a Rav4 Prime.
I stumbled across mine, while flipping through screens on my Prime.
Who need to read those stinking manuals...

 

My RAV4 is a Prime.