The height off the water is pretty immaterial. It was an issue back in the days when leds didn't have dimmers. Now it's just about getting full tank coverage and light spill outside the tank. You'll have some spill because you have lights that get all the way to the ends of your tank, so the spread of 90 degrees down from there will spill outside the tank.
I think you have plenty of light for your tank and I'd recommend you start at about 10 to 20% white and 30 to 40% blue. It's hard to say when to quite bumping them up.
A PAR meter is the easiest way to set the power levels. Borrow one from a fellow club member, ask the LFS if they have one you can barrow or rent, and you can find them for rent online.
I'd suggest you try the 'canary in a coalmine' approach. Get a small frag of a red cap monti and set it in your tank higher than all the other corals. When you raise the light intensity too high, the red cap will start to bleach before any other corals. At that point, dial the power back a bit (5% to 10%) and you should be good to go.
