I am getting interesting results from my vaguely similar set up, at a mere 8 months. It isn't as worked out as yours is.
I get strong direct sunlight from above and behind the tank, and I have really good, red Ludwigia flourishing. I'm not a plant person, and not killing Ludwigia is a first for me. I was kayaking last summer and looking at how the Ludwigia grew in a Canadian small river, and decided to set up similarly. It's working.
I do more water changes than you, weekly 30 percent. I also have the tank surrounded by terrestrial plants. I put a few Aphyosemion poliaki killies in as a single species set up, and now I have a large colony with males showing off in the sunshine - it's a great tank. There's always something going on and the colours of the fish in natural light....
With enough plant growth, I just have to wipe the front glass every second water change or so. I have a sort of wall of emerged plants along the back. In front of that, some Bacopa drifters have settled down and I expect flowers there shortly.