Auto Mode works very differently on mine, in that it drives in EV, untill the battery depletes to 12 – 15% and switches to what I call Auto HEV mode. Even with my latest return home yesterday it got me to the same point 40 miles down the road at 60-70mph, as it has done since my very first family trip since having the car.
As to what I mean by engine fuel mode, I don’t know what triggered it or what variables needed to be met. I simply noticed on the PHEV screen its saying engine fuel mode for three maybe four times for a short period. Each time it showed the battery display went dim and you could clearly see the engine sending power to the wheels only and it wasn’t as if the battery was even close to full or can I see anything in the manual!
On longer journeys, I have also started to turn off regen assuming it uses less fuel coasting, than slowing down with regen only for me to need to apply more throttle to get back up to speed.