So opening the damper about 2 inches and slightly closing the stack damper accomplished it in that instance ?
Further observation
The 2 dial thermometers are irrelevant to the grate temperature but probably are at an offset to the grate temperature
Getting the 2 thermometers reading the same will be useful in adjusting out temperature differences left to right.
Given they are both reading the same, then they should indicate a fixed offset from the upper shelf.
Last question.. given that the cooker is optimized to a temperature point on the lower grate just left of center,
given equal left to right temperature will the upper grate tend to run hotter ,cooler or pretty much the same as lower grate.?
Yoder Course 101