I too have an external Rad. Initially, I had my fans blowing out like yours. My cpu cooling under load did not seem right though. I switched the fans to blow toward the case and got a reduction of 6C.

Use the stand-offs you got with the radbox and move both fans to blow toward the case. NOTE: I adjusted the speed of the case exhaust fan to not block airflow from the opposing rad fan. I use a Bitspower bracket rather than a radbox so I do not need stand-offs.