The KFA2 Serious Gaming Edition has equipped with 1-Clip Booster, which can be installed at the back plate and it is the precision and quality that win. When the fan is at the back the PCB is in fact much shorter than the cooler and the key is to allow air to flow as easy as they could, therefore KFA2 built larger holes that allows air to flow through to fulfill the first requirement.
Apart from that, the advantage of adding a fan on the back plate, the 1-Clip booster fan design sucks the air out instead of blowing the air in, creating a technically-correct push-pull cooling effects. When this additional fan is used, it can achieve better performance as if a GPU running with a normal back plate.