That's sort of where the confusion comes into play. On the return side, there will be a velocity established by the cross tubes farthest from the inlet/outlet. This velocity profile makes it difficult for flow to exit the cross tubes nearer the inlet/outlet.
Here's an experiment for the really curious. Take a length of pipe and drill a few holes along its length such that the hole area totals ~ 2-3X the cross area of the pipe. Now hook a pump up to one end of the pipe and cap the other. Dunk the pipe under water and turn on the pump. More flow will enter through the holes farthest from the pump. If you repeat the same experiment with holes totalling ~ 1X the area of the pipe or less, more flow will enter nearest the pump. It's only when you consider orifice losses and the hydraulic grade profile (function of depth and fluid velocity) that this stuff starts to make sense.
Oh, and your observation about your most recent picture is correct. Highest flow will occur in the center. Deviation from average depends on size/quantity of little runs versus flow and inlet/outlet size.
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