Because it appears your cooker is long, I would move the firebox to the rear.
A bigger fire box where it's at know will creat a really hot spot near it.
It appears you have two pipes from your fire box into the cooking chamber.
Maybe you can run one of those pipes behind the cooker to the center.
-Captain of Barkin Dawgs BBQ
-KCBS Judge #21924
-36" Kingfisher Combo
-New Braunfels Bandera (rescued)
-Weber 22.5" Kettle (rescued)
-A homemade trailer cooker
-Concession trailer nicknamed "The Dawg House"