How low should rockwool be?

I have an ebb and flo system and im wondering should my 1x rockwool cubes be sitting flush on where the water fills to?

should it be above it bone dry with just roots going down into it? im talking about from start.

also should i start seedlings once they sprout directly into the buckets under a t5 light ray?

I am not familiar with your system but I put my cubes one pebble below the surface of the rock. My cubes become totally submersed during watering.

im assuming you meant 1 inch rockwool cubes, and your medium is most likely hydroton or rockwool. you dont want the cube to get soaked you want it about a half inch above the flood line. start your seedlings under whatever, ive had people say you will burn it up under an hps but ive never had a problem.