Ocelaris,
I don't believe that putting the lights on the bottom would be a good idea.
I have read from several books that you aren't supposed to rotate your plants after they start to bloom because the change in the direction of light will make the flowers bloom sideways or even upside down. That is because the flower buds will generally point toward the source of light. (After they are all open, then they can be moved)
If their theory is correct, and unless you want all your flowers pointing down, I'd stick to the side or top for lights.
Just a thought.
Chris