As for your question, based on our testing, the fan blowing towards the U-shaped side would be better (In installation manual, this direction is shown as double circle) but this cannot be always true as each user/case has different components inside and the case airflow also affects on the performance of the heatsink.  That is why the fan for Infinity can be mounted in 4 ways, so you can choose the best optimized direction for your set-up.