But even though the discharge pressure (head pressure) exceeds the height difference which it always has and will, the added pressure of the of the tank height or lack there is cumulative or subtractive in the return pressure chamber which remember is 10 times the volume of the 1.5 inch hose from the pump pressure side. Inside the mixing chamber resistance and or the lack thereof is felt just like the line junction in an electrical circuit.
So is the water inside the mixing chamber going to flow to the to tank with more resistance more water/more resistance or less water/less resistance? Well just like trying to blow air underwater with a hose, the deeper tank is the much more difficult, and if you had a straw with a T junction one end in a glass half full and the other full, when your mouth being the mixing chamber blows, all the air would go to the the glass half full.
However you raise the same question I asked myself and I was thinking of installing 2 additional hoses from each the manifold to the tank, but when you think about it additional hoses to equalize flow are not needed as the chamber should do it all. Just like additional straws would not help off the T to get bubbles or liquid in the other glass, it only can equalize.
Now if a discharge hose got plugged which is almost impossible, then I would be in trouble and a second set of hoses would be wise or overkill depending on how you look at it.
In any case its cheap enough and so non invasive I think its worth a try don't you, or do you have a more full proof and low cost method?