Initially I was going to use far less of the rock and have more 'free' space but the guy I'm getting it from suggests it needs a large amount for biological filtration.
If that's not the case I'll thin it out, keep the corals I like and sell the spare rock and coral.
Ok, it is right in a way. Yes the rock is a good natural filtration method and in the past we did cram as much rock in as we could however with modern equipment we can achieve much better results than we did with just a tank of rock. This is just my take on it, maybe someone else will come along with a different view.
For me I want space all around my rock so flow can circulate 360 degrees of the tank, minimise trapped detritus and allows easier maintenance. Also it give more room for fish to swim and allows for nicer scapes in my opinion. Same with putting rock in the sump, the amount you plan to put in can be replace with just one filter brick like this
Skimmers, ALR's, nitrate, carbon, phosphate reactors are all available to allow us to maximise and ease keeping marines.
End of the day this hobby is about one thing, Keeping water. If you can maintain good water then you can keep anything in it. Like I said just my opinion mate