Hi, OP, from another foodie homesteader in BC!
We produce a lot of our own fruits and veggies and keep chicken for meat and eggs as well. For 2 of us, I think we average $250-350/mo in luxurious groceries, and then maybe another $100/mo at Costco, and then we also probably spend another $400-500/year in bulk food supplies (salmon that we freeze, a friend's canned fresh and smoked tuna, beans and other pantry supplies). So I think you are correct, that $225 or so per person per month for active adults and teens is actually not bad. Zikoris and others who are getting closer to $150 per person are usually in larger cities with a wide variety of cheaper shopping options like ethnic grocery stores.
I would say, though, that in my experience, there are still things we can do to *optimize* our spending, but at this stage, it's really about optimizing what you're eating to match your desired spending goals. To bring grocery costs down, we all really only have a few options: 1) grow/produce more of the food you eat; 2) spend less per item for the food you're already eating; 3) eat foods that cost less.
It sounds like you've probably optimized #2 for your options and lifestyle. So that leaves 1 and 2. My suggestion would be to really make sure you are eating the food you have produced and are producing the food that you're going to eat. About this time each year, for instance, Erica at NWEdible (she's on these forums and also has a great website if you google) does an "eat down your larder" challenge to clear out the stores from last season and get ready for the season to come. I know intellectually that I could live happily on our stores and garden for months at a time if I had to...but I know I don't have to, so off to the store for that avocado and lettuce I go! :) It can be useful to really force yourself to eat out of the pantry and freezer and find recipes that work for the ingredients you have, if only for a month or two.
Next, it was incredibly helpful to me to take stock of what we are actually eating over the course of a week (including snacks, drinks and all meals), and price those out. This really helped me to see that our meal costs varied widely, from almost free to really expensive. Now I'm in a much better position to make sure that we eat more of the cheap meals and fewer of the expensive ones. It also showed me just how much we would save, for instance, if we started making our own bread again or whether I should find a cheaper substitute for x ingredient.
Do investigate big bulk buying, too, as someone else suggested. We have a bulk foods store in our area that lets customers piggy back on there wholesale order once each year. We've bought grains, beans, nuts, etc through them at huge discounts in multi-year quantities. We keep these in airtight buckets and won't have to replace them for some time. The key, though, is to buy those things that you know that you'll go through--nothing worse than having emergency foods that you never eat!
The last thing to do when you take stock of what you're actually eating is to re-plan your garden with those foods in mind. After a number of years at this, I still tweak regularly, of course. But this is the data you need to decide that yes, it is worth buying a dehydrator to dry apples for snacks so you don't have to buy dried cranberries for the winter, or how many pints of tomato sauce need to be put up each year. The more you are conscious of your food production and storage as the major planning of your food supply, the better. Sharon Astyk's book, Independence Days, is quite good for tips on this, if you haven't read her stuff already.
Having done these things, the biggest gain we have gotten is that we simply are hardly in grocery stores, and this has removed a huge amount of our impulse buying, which was a big weakness.
All that said, even having done all these things, we still spend pretty close to what you are! :) And that is ok with us. We know that we are living an incredibly luxurious food life, and we are totally ok with that. BUT, we also now understand that this is luxury, and there are many things we could cut and still have happy, healthy diets. I think all families should get to a balance that is right for them, but it's really nice to know you are making the conscious choice to spend a little more, rather than just always feeling inadequate for staying on budget.
Good luck!