TWI

I have now owned an 08 Lexus RX400h for 2 months and put about 1500miles on the clock. Although the overall driving experience is great, one thing I am not very happy about is the fuel consumption. I do not drive like a particular loon and I have had a mix of motorway and urban driving. Average consumption since I got the vehicle is 24mpg!! Also it seems that often the petrol motor kicks in at anythign over 10mph. On the vehicle I test drove it seemed to kick in around 30mph..could this be the reason? Should i be contacting the dealership to make demands or is this just the difference between marketing hype (31mpg+) and reality? If latter then I wish i had my BMW 535d back as I chose the lexus to improve my fuel efficiency..