I am sure you already have, but in the off chance you haven't, try moving the base of the smaller brach to the far left front corner and angling the larger piece with it's base in the far right corner. This should create depth...at least in my mind it does. Hard to know without seeing it. Another thing I would try is turning the base up, placing the base in the upper corners in a way they are "out of view" if possible. This good give a neat effect also with the branches giving the illusion of hanging in the water from a tree on "the bank above".
Anyway...just some thoughts to try and help you achieve depth. It took me awhile to get my wood just right. Seemes I was tweeking it every time I walked by the tank. Finally I'm happy with it. Just keep playing with it until you find "it"
I love both pieces! Your tank will be so cool when your plants finish up the last touches!