I have a pet peeve. I don't like having things pushed against the viewing panels (all 3 of them), so the border area is kind of off limit for anything. I can make the border less boxy looking but that border has to stay.
As for the pebbles, I like the look of it in the middle around the wood (you probably can't see it in the picture). As for the borders it does look off to me too. But it was either this or the bright orange. My feeling is after that orange patch in the middle is covered (and also the column on the right), the pebble would look less like a frame and more like the ground.
Do you mean the foreground stem plants? I agree it looks too neat to be natural. To me it looks like crops growing in the country side. But that may be the direction that I seem to be going. I do think that patch of plants can be improved. The problem lies in I don't seem to have anywhere else to place them. Which is why it is in a neat row. As mentioned I can't push it to the side. I also can't push it to the back as the area is shaded by the anubias above (in the photo you can see that it is black, and I filled it with pebbles).
I also dislike the right rear corner, which to me lack definition. In an ideal world, I would remove the wisteria and move the bacopa in the middle to the back. Then I'll have a large piece of moss wood to cover that area along with the "hole" that I mentioned earlier. But I already have the plant, and in the short term I need good nitrate absorber like this.