Do you have the radiator fans as intake? Does that yield better temp results in your build?
I have fans oriented in the more common orientation (seems to be more common anyway). Meaning, the fans pull air from the case and exhaust out of the top panel. Drawing air from inside of the case means the mesh sides and bottom panel are all sources for intake.
Edit: this is the same fan orientation as @fabio so I don't have any novel thermal data to contribute. Just an observation on dust accumulation that illustrates where the most flow through the mesh is.