I've done a lot of experimenting as well with multiple thermometers , without a diffuser , regardless of how I load my charcoal basket(which is 17" wide) it runs 50 degrees hotter in the center than at the side of the drum. I have a second grate 6 inches down , I have tried a clay saucer on that grate and I wind up with much higher temps around the edge of the saucer with a cold spot dead center. I attribute that to the saucer being too far from the fire , too close to the meat. I'm certain there is a sweet spot as far as diameter of the diffuser and distance from the fire that will make for really even temps in a UDS , I just don't know what those measurements are. When I first joined this forum , I read the entire UDS thread , there was a guy on that thread that was cutting out diffusers with different hole patterns and checking how the different patterns affected the temps. I followed it very closely but nothing ever came of it. I think if someone could come up with a solution to the uneven temps in the UDS , such as "you need a diffuser of X dimesions at X distance from the charcoal basket" it would be a major improvement , for an already awesome cooker.