It’s true, the Kuga has a bigger battery and in the test Glos Guy refers to the fuel consumption came out a lot better because the test mileage was quite low. If I remember it was little more than double the battery range The first XC40 I test drove did 24 miles in hybrid mode, mostly town traffic, the second did 20 but that was taking it straight out onto a dual carriageway and 60 to 70 mph. The battery size is quite small and the car is heavy.
The whole question of the economics of PHEVs is complex and very dependant on patterns of use. The cost of the initial electric charge seems rarely to be considered when a PHEV is said to do a particular mpg. I suspect we’ll save on running costs with the Volvo we’ve ordered compared with our current X1 but it’s not the primary reason for choosing it.