Arbittan, from your posts you seem to expect the car to deliver the rated mpg regardless, even though the ratings cannot possibly be accurate for everyone. It is simply an estimate. When you posted the mpg on the sticker, you put that it got "41/51." The numbers actually are 41/45. Still, with an average mpg of 43 overall, your 35mpg is rather low.

Something very important with mpg is not only the driving habits, but the driving conditions. Are you in the city, crawling at 10 mph, constantly having to slow down/speed up like you were on a see saw (best analogy I could think of) at a snail's pace? I don't think you'll get optimum mpg like that; for that kind of low-speed driving a Prius would be better. Now, do you drive at 80 or 90mph on the highway with the trunk loaded and a bicycle roof rack? Like that you won't get optimum mpg either. Optimum mpg in a Honda Civic hybrid is with steady highway speed driving (50-65, maybe 70mph) and without bicycle racks or a loaded trunk. If you drive in the city, optimum mpg would probably come from conditions that allow you to drive 30-40mph and coast plenty.

If you drive under optimum conditions and still get bad mpg then something is wrong. Tires, IMA, transmission, engine? Now, I don't mean to insult you, but it could also be a simple mistake of numbers. Maybe you put down something wrong with the gas reciepts, or perhaps you read the odometer wrong because of tha trip A trip B thing? It's just a possibility.

I cannot confirm for absolutely certainty what I am saying because I do not own a Civic Hybrid, but I do love the Civic Hybrid and IMA system and learn as much about it as I can. Hope you find out what the reason for the low mpg