Your aquascape I think looks great as it is. You're vision is how it will look in the future and how easy it is to maintain around everything.
Firstly the quantity of rock will not impact this phase of your tank, it's only when you have a high bio load you might need more filtration.
What I have done is rather than compromise my aquascape by adding twice as much rock in as I would have liked, was to add Bio Sphere's into the sump to make up the shortfall in rock.
Why does BRS recommend this? Biological filtration is the number one key to a nice and stable reef tank, and anytime we can sneak in some MarinePure Biomedia into an All in one tank, sump, or even overflows we will. We have run density tests and they have proved to be more porous than any live...
www.bulkreefsupply.com