I had the same problem.
The only way I could get my aeration to work was to put them on every return. Water will seek the easiest path, so as long as you have those other three easier paths, your aerator won't get much pressure. I had great aeration when all the returns were doing it, but no circulation! I was using aeration to raise pH, so it was temporary. The only idea I had come up with to solve this, was to run a separate pump, like a sump pump, to an aerator, and leave the returns alone. But my TA/pH adjusting was done by then, so I never pursued that. The plus to the extra pump idea would have meant I could aerate without having to run the main pump.
Some pools have plumbing that has a valve for every return. Those lucky ones can adjust the pressure to each return separately. But I think most pools have all the returns on the same loop, no separate valves, so we're kinda stuck. I dunno. How are those with aerators shooting a dozen feet in the air getting those to do that?
One possibility... sometimes one return works better than the others, because of where it is in the loop, maybe closer to the pump. You could see if one of the other three returns works better. But if there is one, it won't be by much.
Or possibly... you could fashion a jet for each of the other three returns that constricts their flow. Some PVC gizmo that reduces each to a lesser flow (smaller pipe, cap with a smaller hole, ball valve?), so you'd still be able to get circulation from the other three return, but they'll be reduced such that the aerator receives more pressure.
