How high should c02 hosing be above canopy

Hi all, I have a 20 lb c02 tank that is connected to a regulator and I have calculated out how much c02 to pump into my room every hour to get close to the 1500ppm that is recommended for optimization. My question is how high should I hang the tubing that dispurses the c02 above the canopy? I have the tubing basically at the canopy height at this point but I know that c02 is heavier than air and will "sink" in a room. I do have fans running to move the air around a good amount but pretty much the air circulation stays above the canopy, its thick! Should I raise the c02 lines higher up in the 4x4 box I'm growing in or is it fine to have the tubing at the same height as the canopy?

Thanks in advance for the advice!!

Great question. I would like the answer too as I have the same set up.

I have mine on the ceiling with a fan in front of it blowing the c02 down into the canopy. And a fan on the floor blowing it back up, try to arrange the fans into a circuit.

http://www.hydroponics.net/learn/co2_calculator.asp