I could be way off base, but based on my experience with my #3, I think they tend to average about 10 degrees below the thermostat temp.
When I smoke a butt at 225, my smoker temp (as gauged by my Maverick ET-733) range is typically about 190-220. So, I am rarely if ever breaking the 225 mark that I have my thermostat set for. Based on the numbers from my 733, I am guessing my average temp is closer to 210-215.
I typically place my smoker probe clip on the bottom of the rack that has my meat on it equally distant from the meat and the wall of the smoker.
An Auber with a permanent probe is definitely in my future, which I think will tighten this up. But in the meantime, I have had nothing but great smokes setting my dial to 225, so I am not going to sweat it.