A:Answer I'm not sure if you mean by back fan as in exhaust from the case, or two fans on the cooler, even though it comes with one, which creates a "push/pull" cooling solution?
I can answer your question easily however because I did both in a Corsair 4000D Airflow case, with 4 RAM sticks, so from the front of the case to the back, from This cooler back in that area belongs to cooling fans and fins, but i must say adding a second fan to the cooler helps a lot, and they supply you with a mount for a second fan which also adds "unofficially" but tested by me an extra 30-70 watts of thermal capacity than with just one fan.....
One of the better advantages also to having 2 fans most people would say more noise, but that's actually less noise as you are using the fans at lower rpms. Personally I find Noctula 120mm redux 17's to be the best fans for everything that is not RGB!