Aussie, I know you've read a lot of the posts on how to attain better mileage, but just a couple of suggestions. If you haven't yet, be sure to read Hot Georgia's article in the Learn section. Also, it is important in the HCHII to make sure you're not using the A/C. Rule of thumb, if the words A/C OFF are not displayed, do not assume that you are not using the A/C.

If you're getting 51.2 mpg, you're doing a good job and better than most! Unlike we here in the northern hemisphere, many of us bought our HCHII's either part way through winter or into spring. You've just gone through fall, and are now into winter, right? So what type of temperatures do you see there? Are you in the section of Australia that has a Mediterranian climate, or do you see pretty cold weather? You already know that cold weather kills mileage...