As mentioned, you can create separate SSIDs for 2.4 and 5. If you want to have a combined SSID as you have now, you may wish to adjust the power settings for both 2.4 and 5. For example, set the 2.4 radio power to 3db and the 5 to 15bd - adjust power settings until you get an acceptable result for your environment.
From the log provided, it looks like the 2.4 radio power is quite high.
All this is assuming that wireless card drivers are behaving somewhat correctly.