Ok what I would do is put the two rock piles to close together and then connect them with a rock to make it seem like one wall, but I would offset it to the left or right to make room to add on with more rocks and also when it's offset like that it causes the eyes to wander around the tank instead of staring at one point (the middle). And just play around with the rocks try to space them out a little to allow more flow through them, and more hiding spaces for the fish it's also adds more contrast when your looking at it. But hey that's just what I would do you absolutely don't have to because it's your tank and your the one that's gunna be looking at it the most so you should do what you really like I can only give an opinion you do what you want with it