the problem is airflow;  the cards want to push the air out of the back of them, so if you have them mounted facing both directions, you are working against that flow with the ones mounted in the mainboard (as one is in this photo).

I need to repair a riser so we can mount that one card with all of the others.  Till then, it sits there;  Its being run open-case with a fan blowing down on it from the top.


Higher flow fans are needed for the front panel.