The way that I had my original arrangement is the highest that the large rock can get. I tried playing around with other positions but it's just too off-balanced and I'd be afraid of it tipping over and doing some serious damage.
I actually dabbled around with some center-focused arrangements before coming up with my second design. However, my only gripe with having the large rock in the middle is that it no longer conceals all the tubes, airstones, heater, co2 diffuser, etc. that I've hidden behind it.
Also, there's a perspective issue because people will be viewing from the center and from the side equally based on it's placement in the room. I actually consider that wall along the side to be the back of the aquarium which is why I put my rocks along the "back".
I'm going to play around with a few more center-oriented designs during my lunch break but I probably won't post any pictures of them unless I can find a positioning that agrees with me personally.