I've been doing some random reading on other forums about live rock. Many reefers are now realizing that the total lbs of LR isn't really as important as available surface area to grow bacteria. It's almost getting outdated like the watts per gallon formula...it's just a general rule of thumb. It's the premise that more rock provides better filtration. Well, that only goes so far when the rocks are packed so tightly togeher that water movement is compromised. It can then becomes a trap for junk and waste. I think a more open aquascape with good water flow and tons of nooks and crannies for bacteria to grow is the optiomal goal to help with filtration.
You can have one 10lbs piece of fiji rock that is pretty much a solid chunk and then you can have that same 10lbs of a more pours rock that will actually provide more useable surface area.