Where to place diff. plants under light?

I have an indoor growroom in the basement. I started with a shelf system 
that has four 4 foot flor. bulbs under each shelf. I then bought a MH 
400 and hung it in front of the shelf, and got another shelf to put next 
to it. So, basicaly there are 2 selves on each unit that get nice light 
from the MH, along with the one shelf that has the flor. bulbs.
My question is- what plants should I put closer to the MH? I know that 
the Paphs and the phals need to a be little furthar from the bulb, but I 
also have several other types. I grow:
Brassavola
Cattleyas
Oncidium
Dendrobium
Brassia Hybrids
Oncidium
Degarmoara
Miltassia
Odontocidium
and the Phals and Paphs

I know this is a list of very different type orchids- but they all seem 
to be doing great under the MH/shelves. Once they spike I bring them 
into a bow window in my living room. I have had to move some around 
under the MH to prevent burning, etc., and I am trying to keep humidity 
up. I have only had the light for a couple of months.

So, my question is this: does anyone have any recommedations as to what 
plants should be closer to the lights- and which should be furthar from 
the light? I want to make the most of the space, and put the 
light-loving plants closer to the MH.

I will post some pics on a site, if anyone wants to see the space I 
made...