the people who have written many words and been published on paper say the return should go into the top hose so it then gets cooled.
I have never in the past done this I have always taken it to the bottom hose.
I have now plumbed it into the top hose. if this makes any difference or not I don't know yet.
so info I have picked up over the years.
1: when plumbing into the bottom hose add a restriction so not to much water goes that way. I never did that.
2: you don't want uncooled water going back into the engine. it is not uncooled as it is cooled by the cooled water from the rad.
3 plumbing into the top hose puts more water through the rad so it will not cool it as much.
so to sum up both ways work just as well.
on the last cars they had a switch to stop the flow through the heater. this diverted the coolant straight to the bottom hose.