Aquascaping..
I placed alot of thought into the structure I wanted and not only to be asethically pleasing, but also If I needed to catch a fish, cleaning the glass, flow (dont want any dead spots), size of caves, future placement of corals, zoa's etc....
Placing rock on back wall of tank overtime in my opinion will lead to deadspots and a haven for waste to collect.
Placing the rock in the center with overhangs, caves etc.. will allow for viewing pleasure on all sides, good flow and fish can be seen swimming in one side and out the other, something that cant be accomplished with stacking rocks against the back wall.
With my layout, the rocks are basically centered in the tank and pretty much runs the full lenght of the tank, but one end the rock sort of curves in towards the front of the tank to give it a slight "j" shape. There are just so many options, do want works for you both in function and asthetics. Just my opinion.