With what you describe, what you get is about right.
During the day, heat (a/c on and it can get too hot and start dropping efficiency in my experience) traffic (lights and driver's who don't understand momentum conservation in front of me), road work, and maintaining flow of traffic, I have gotten in the 42 range, I saw it dip under 40 once and had to change my route. But even without that I did manage to get it back up just by learning the pattern of the roads. If I know I am on a 2-lane, and people turn a lot, I put more space and watch for the signs of a slow down or stop.
If I drive the same roads at off-peak times, which gives me NO traffic, catch all green lights, and maximize momentum ... I can get nearly 70 mpg with no major efforts (even with the a/c running), this is about a 6-8 mile one way commute from a cold engine.
I don't FAS, or anything really special. I have learned how to drive as close to 40 mpg with assist while accelerating, get up to speed a little quicker if I have a hill/overpass just ahead of a red light, but in general, I have learned how to use the least amount of fuel to maintain my speed. I do maximize charge without friction brakes as a general practice. It helps me keep a more smooth driving approach and have slowly gotten better timing from this easily performed passive driving technique. I use more assist than some others, and I try to make up for it in other areas.
I have found 80-100 mpg easily attainable at 45
mph if the road is of good condition and the temps are right. I will admit, my car seems a bit quirky, sometimes I seem to be able to climb slight inclines with 60+ mpg, sometimes flat ground it stuggles to do the same. I do have tire pressure between 55-65 depending on my mood. I have taken the advice of another and get just a little above the limit and use that gap to get the car at a steady speed.
I would say take some time out, find a nice smooth road with some sections of varying conditions (flat spots, rolling hills, etc), with little traffic (usually at night) and just learn your car. Get on an intimate basis on its particular behaviors, and find out how it wants to be driven best. That is what I did. I found a state road with light traffic at night and took a few 100+ mile round trips. I was very happy the first time I found a 10+ mile stretch I could maintain 80+ on the instant, then I learned that I could get it to 120 and hold it with more experience.
I feel driving a hybrid is the same as anything, the more you do it, the better you get. If you were to go to an autocross event, each time you run, you learn something new ... or do as you are now, and ask what others are doing to lower their times. I believe you may be able to surpass the 40s with a/c if you can find a good place to get some good segments under your belt.
Are you absolutely certain you have 0w-20 in you engine? are you at least at the reccommended pressure or higher (cold)? Are you due for any fluid changes? Do you carry any extra weight? Do you still have the low rolling resistant tires? Have you tried a fuel treatment injection cleaner lately (not saying they work but maybe worth a try)? Is your route in such a way that it creates forced regen (which it is still possible to do 60+ with it)? Waxed your car (j/k

)? Can't think of any other particulars that can have an effect at the moment, but if anyone else can ... oh, have you tried different shoes? I know it sounds funny, but some of my footwear makes it easier to control the pedal pressure than others. On a LONG trip sometimes I go barefoot to get a better feel and more control ... Managed almost 70 mpg on the interstate just with controlled foot pressure. Maybe listen to some relaxing music it helps some. I would definately not put on a 'racing' mix tape
It is possible to get amazing things out of these cars in near perfect conditions, but over 40 in traffic and heat ... is still quite a feat to do in my eyes.