You don't really need to pass any air over the PCB, though. Anything that needs cooling sticks up above it. Also the airflow through a case isn't perfectly para

You don't really need to pass any air over the PCB, though. Anything that needs cooling sticks up above it. Also the airflow through a case isn't perfectly parallel to the motherboard PCB anyway. GPU fans throw the air in all sorts of directions, including straight down into the motherboard. And so do CPU coolers. Cables also don't really obstruct the airflow like at all.