What kind of weather/temps? What kind of terrain that first 10 minutes? Are you using AC or does the engine need to warm from cold temps? Have you tried 'feathering the pedal' to achieve stealth?
Certainly the first 5-20 min. will be the worst time for fuel efficiency, but if you are in a moderate temperture area, relatively level terrain, and the situation you describe ALWAYS occurs then I suggest that there's something very much wrong. I've started with the ICE quickly kicking in 3-4 times, but almost always I'm able to start with just the battery, back out in stealth, then when I start forward the ICE kicks in (regardless of battery charge status)--presumably to warm the engine and coolant.
After even a brief 3-4 min drive I'm able to achieve stealth and maintain it on slight downhill grades at speeds up to about 46mph (56mph after well warmed with near full battery), and even on level ground can feather into stealth up to 42mph if maintaining a steady speed.
This has gotten easier and easier as I approached the 600mile mark.
I think everyone's results will vary, but if you're under 'normal' conditions and still seeing the milage you described and no stealth then I'd take it to the service shop to have it checked.
--evan