I have found the reverse to be true on my WSM 22.5.... If and when I lift the cover I don't lose temps, so much oxygen enters the smoker, that temps sky rocket to over 325 almost instantly. Then I have to close all four vents, and force the temp back down (careful not to choke the fire completely) to about 250. Then re-open the top vent to half, & one lower vent (away from the wind) to about 3/16" open (very small crack), and let her smoke.
I never could understand some posts I have read on this site, when they declare that their smoker has all the vents open, and temps only reach some 250 degrees. I'm forced to cook (starting at 200) with the top vent half open, two lower vents (towards the wind) closed, and the remaining vent (away from the vent) closed to within a 3/16" crack (folks, that is small), plus an empty water pan. Even with those settings, My temps are still right at 255/265 (ET732 grill measure). I have never been able to achieve that low & slow 225/230 cook....