Haha! That's the way.
I don't think you can call this Iwagumi, but who cares? Looking much better. It's almost as though it's a scene from a south American jungle with Mayan pyramids.
IMO the first way you had the RHS rock stack is more fitting with the man made look. The second is more natural. So I suppose it depends what you are looking for.
I think you can get away with it the height it is. You could also make it higher. I think it would work either way. But I'm certtainly leaning toward you making the right just a bit bigger to.
To me, if it is kept the same you really need to lower the substrate a bit. Not too much, and not at the front but because the rocks down the bottom are really nice, it would be a shame to cover them. I'd be looking for plants that don't grow very high at all near the front and sides of the rock. Perhaps some taller ones at the back. I can really see a jungle clearing with an ancient ruin.
I'll comment on the plants you have suggested, but purely based on looks, I know little about individual plants.
Hottonia palustris, is nice, but I'd only put it in the far background as I'd imagine it grows tall pretty quick.
Hydrothrix gardneri, same with this one, mix it up with the others perhaps. (note it says very fast growth).
Downoi, Perfect plant IMO. Hope it's suitable. You could plant it in the very foreground and against the sides of your rocks hear and there.
Ranunculus Inundatus, Again, awesome looking plant (ooo, it's Australian, I'll have to find some.