I'm buying the same case, i figured on a side mount cooler pointed towards the back since the fans pull air in from the front and sides and mostly exhaust out the back. Are you placing any fans in the 80mm slots in the back?
Careful with fans on the Silverstone cases they use a positive air pressure design for cooling. You need to do it right or it's worse not better.
Even though Silverstone labels the 80mm rear as exhaust, I have had best results by actually using 2x80mm rear fans as INTAKE with this case. Idle temp dropped 7oC and full load dropped a good 15oC. Using all 5 120mm as intake as well but my cpu cooler is vertical fwiw. And maybe good push/pull air circulation with side mount cooler oriented towards the back...you'll have to experiment to find the best fan setup...