If you like that rock I say keep it that way regardless of how close to the surface it is. You can mount corals all over the sides. Check out the thread I think it's called my Algea Farm, it's an amazing tank. Some big rocks close the surface not 6" but covered in corals. Some LPS mounted upside down on the bottom. Some of the corals are growing right to the surface of the water. You would just need to acclimate to the higher lighting up there and should be fine.
Thanks for the vote of confidence, although I do like to see tanks with minimal rock so I still may lower it a bit. I couldn't find the thread that you mentioned but I would love to see it so I can imagine the potential of my tank.