Why is the reasoning for putting the miners up high, just to get them out of the way? They'll run cooler if they are pulling in cool air down at the bottom of the barn, the hot air will naturally rise to fill in the head space at the top and then you can vent it via a ridge vent or some gable vents, or vents at each end of the barn up high. You say that the "air can go far", but warm air travels vertically, not horizontally.
well the miners are pulling air in a way that works fairly well.
hot air does rise but the fans push it forwards so the real heat moves out and up.
next time I go I will bring the infra red gun and show that intake is far cooler then it looks.
the goal is passive cooling at 0 cost.
the full setup will be 8 ½ miners the ½ is a full case with a dead board.
I have an idea which may provide passive cool air or 1 fan drawing in cool air