Thanks for the comments everyone.
Here is the most recent change using Kathyy's advice - and it makes sense as the area under the driftwood in the corner will get very little light. Here is what I came up with:
But I agree with you Jellie - that the back right corner looks empty. But, there is substrate sloping in the tank - it just doesn't show great from the angle I take the front shots. Here is a side shot. I think the slope will be better emphasized when I plant it - it is only a 10g tank - and I don't want to go much higher on the substrate as some of my back plants will be taller. But I will see what I can do about the right hand side.