This is what I have been getting - 90% urban driving with short journeys. Start-stop works well most of the time. Been told that my car has Eco pack as well but don't know what are the modifications because of that in the car.
That's about what I get when there's traffic. Same route, no traffic (or speeding) will get me 53mpg because I usually don't have to brake at roundabouts.
Regarding ISG - I really don't think it should be activating at all until the engine gets to normal temperature. Stop/Start seems unlikely to prolong engine life prior to those conditions but YMMV. Apart from that, once the car is up to temps it seems OK but I confess to turning the fan from 2 to 3 when the aircon is on just to stop ISG