Typical front-to-rear cooled enclosure systems (for vertically-mounted cards) have the axial muffin fans in the rear of the enclosure.  Not only can this affect rear I/O space and potential increase the height of the chassis, the cooling is less efficient.  With that approach, the airflow path has to bend from the front of the enclosure, turn 90 degrees and go up the cards, and do a 2nd 90 degree turn and go out the back.  This "S"-shaped airflow path is not ideal for effective cooling. 

With Pixus' Rittal-brand reverse impeller blowers, we can eliminate one of the 90 degree bends.  With the intelligent, separately hot-swappable fans directly above the card cage, the cooling is more efficient and effective.