Greg some rules to satrt with regarding Temp variations. yours would be a little different than mine cause your horizontal is a little longer, but....
back to center on the bottom shelf is 40 degrees cooler than the thermo. Top shelves slight higher than the thermo. I keep my thermo around 260 knowing the food is about 220. top shelfs would be around 260-270. Closest to the firebox near the hotspot, about 50 degrees hotter than the thermo.
I just keep the thermo around 250-260, and move the food around based on what I want..
Temps in the vertical are pretty even all around. BUT,a nd a BIG But.. Verytical, with the baffle installed 50-75 degrees cooler than the horizontal, remove the baffle and its 25 degrees cooler. I have just strted using the vertical for cooking. Does and excellent job on beer can chickens and whole turkeys.
And another thing i learned after a year of experimenting. Remove the baffle and the bottom shelf of the vertical is really just and extension of the horitontal chamber. Great place to finish ribs.