" Plus the two stacks of seven RP's are all diagonally " its amazing how much a small slope on the board will increase airflow via convection. Way back in the day I ran a lecture capture systems at a University. we had 6 dedicatited capture boxes in a rack which kept overheating. I bent the brackets so rather than flat they sat at a 30% slope and all their temps drops a full 20dec C with no other active cooling.