The light is definitely not even in my tank. Mainly because I'm a total numpty and bought the wrong size LED units. So the lighting isn't likely to change anytime soon, because they also last for ever! I have 2 light units. The one at the back is as far as it can go to the left of the tank and the front unit is as far right as it can go.
I did wonder if light could be the issue, but it is only that front corner that has less light, the back corner should be fine and the tiny plants go all round that end of the tank - it is only as you get behind the bogwood that they've grown.
Perhaps it is just a combination of all factors.