I find a more relaxed driving style helps - even in petrol mode coasting in B0 will help as the engine will shut down if left long enough. So be prepared not to keep at a set speed and allow the speed to tail off before hitting the gas again to wake up the engine. However, I also find using the cruise control more economical than my right foot on motorways.
Food for thought.....I did a 80 mile each way trip a few days ago and managed to get a 13 amp refuel overnight before my return. This trip is probably about 80% motorway.
On the way 'down' I decided to use the cruise control and set it at the breakneck speed of 60 mph (a rather more stunning 96 for our Continental readers).
As an aside I read most of the threads on here and noted a graph from Anko recently in response to a question (I think) about the 'sweet spot for engine rpm re charging and so on. It appeared to me that the 'sweet spot' was pretty much in the area that motor manufacturers for many decades have known was the most efficient speed for a car, namely precisely 56 mph (89.6 kph) and that, going back decades, was the speed at which the best achievable fuel consumption was achieved.
Assuming that the laws of physics haven't changed a lot recently imagine that Mitsu decided to pitch the PHEV's most efficient charging rpm at that which it might be turning at if engaged to the front wheels at precisely 56 mph (my vivid imagination has been marvelled at for eons!)
With this fiction firmly set in my mind that is the reason I set 60mph on the CC (speedo exaggeration + ease of setting = close enough!)
On this trip on the M1 we enjoy a fairly long 50mph section (both ways).
Anyway, whilst actually using the CC and after we had become a petrol car (not long - 12 miles then save engaged- in the current temperatures) I was getting a bit depressed watching the fuel consumption heading steadily south and started trying to play with the brake paddles. You learn something new with this thing nearly every day and I don't know why it surprised me to note that whilst the CC is engaged you can't select B1or B0 (I know...but it took me a couple of seconds to figure out why).
I disengaged the CC and started managing the energy myself (including using regen braking) and the fuel consumption stabilised and occasionally increased to 50 mpg and slightly above. I had engaged 'save' with 5 miles range left.
Had a couple of local jobs to do after arrival but before charging and was down to 0 range.
On the way back didn't use CC at all and when we went ICE decided to use 'Charge' as the motor was running anyway and apart from a few overtaking manoeuvres kept pretty much to 60 mph again.
Cancelled 'Charge' when 12 miles range achieved and upwards progress appeared to have slowed, as expected (I'm hopeless at reading the number of bars on the battery icon).
Hit 'Save' again at 5 miles range remaining and removed that when entering our town limits.
Arrived home with a mile or so range remaining and average fuel consumption for the return 55mpg.
I was quite pleased even though there was a steady southerly over the period that would have hindered the first leg and favoured the second. Otherwise the conditions, temperatures and traffic densities were pretty much identical.
In both cases the fuel consumption figures were stable on arrival, in other words they were sustainable over longer journeys.
Unscientific yes, no readouts or graphs, but, as they say, mustn't grumble!
I do not question but merely seek enlightenment.
'16 GX4H, Orient Red, Gen 3 Glasscoat, Bonnet Lettering, Chrome Pack, Protection Pack, Front and Rear Sensors.