Here's something of my experience. My first drive, I got 40 miles mainly A roads and M Way. I almost did the trip to work and back, and if I hadn't made a short diversion to a shop, I probably would have, the ICE came on a few hundreds of yards from home. Since then it's dropped to around 30. Part of that is the falling temperatures and use of pre-heating, I got mine mid December when it was still quite mild, another part of it is my driving has got less conservative as I've got used to the car, especially the automatic transmission.
As an example of the power used by preheating. Yesterday, the car was iced up and I needed to go out unexpectedly. I turned the preheating on to warm it up and de-ice the windows. 5 or 10 minutes later, the windscreen was starting to thaw but it'd lost 7% of charge so I decided to scrape the ice off manually. The trip was quite short around town, and with stop/start traffic and the cold temperatures, I came home with 49%.The car is showing 31.1 miles for 100% charge.
With a theoretical range of 44 miles, losing 5 or 10 percent of charge due to preheating, and the same due to stop/start traffic and the impact it has becomes significantly range limiting.
I agree the way range is shown its a bit confusing. I don't know how the "average" range it appears to show is calculated, it could be overall average since the car was new, 100 mile rolling average, or based on the journey since the last charge as suggested, or one of a number of methods, and they all have their disadvantages, notably with different drivers with different styles, or when very different journeys are made. In those instances sometimes the range won't accurately refect the drive being made, causing the ICE to be used.
On the other hand, if it showed 44 miles range every time I got in the car, and then a mile down the road it dropped to 36, and after another mile it showed 30, (based on the reality of the journey and driving style) that wouldn't be very useful either.
Overall, the way it displays range gives you a good idea of real, achievable performance. If it shows 31 miles, and my journey is 25, then there's a good chance I'll make it on battery power as the range showed uses real consumption including heating, and driving style. If it shows 31 miles and my journey is 35 miles, I know there is a chance of doing it on battery if I drive carefully but I'll probably do some of it on petrol.
Personally I think the way it's done is useful but what I would like to see is instantaneous range or consumption for each driver or each style of journey with the average being calculated accordingly, ie my wife's average is kept separate from mine (the car does profile's, so why not?), and my M Way average is kept separate from my around town average. It would be way more useful to know I'll get 40 miles on the MWay, and 25 around town and my wife will get 38 on the M Way and 23 around town, rather than being shown an overall average for all journeys made by both of us of say 31 miles. If the satnav was used to plan the journey there's no reason why a prediction of charge consumption couldn't be made at the same time.
The current range display is only a guide, and as such is not totally reliable. There's been a few journeys when the satnav has shown 10 miles to go, the range has shown 8 but I've completed the journey on battery power.
Overall though, I'm disappointed with the real world battery range, after all, 31 miles range really isn't much, I think much of the disappointment expressed above would be avoided by a bigger battery range more suited to real world UK driving conditions.