I'm a real stickler for cohesive/structural looking live rock...having spent 3 years arranging mine and still not satisfied. So, my advice would be to move things closer together, getting a bit of negative space going, follow the "rule of thirds" and just experiment. If you've got a beer, and you're into that sort of thing, inebriation has been shown to increase creativity in studies. Just don't go overboard...to creative and you'll think the live rock will look better outside of the tank.