Indeed. Internally mounted rads will generally perform much worse than rads that can take in fresh air. I had a rad attached directly to the back of my case before, and the temps were..meh. I started using a spacer to block the hot exhaust from the rad, so the fans actually take in fresh air instead, and it dropped the temps by ...at least 5-8 degrees.
One advice would be to increase exhaust capability of your computer, making it a negative pressure case. It would help with the temps.