CO2 effect one part of a tank?

Why not have one filter return at one end, with it's inlet at the opposite end? Then reverse that for the other filter. I would expect this to mix the water much better from end to end. The CO2 concentration does vary a lot from one place to another in my tank too. I have my spray bar blowing back to front at one end of the tank, with the inlet at the other end at the back. I figured this would give good circulation, but I'm finding that the CO2 at the front corner across from the inlet is significantly lower than other areas. I can tell this because the fish that don't particularly like having CO2 in the water are more clustered in that corner than any other area, and my drop checker there reads a green-blue-green, where with everything else the same, when the drop checker was at the other end, it read a strong green to yellowish green. I don't see any other effect on the tank, but it does make me wonder just how possible it is to get uniform distribution of CO2 in a tank.