What I like to do is make the fire box (FB) to cooking chamber (CC) opening (Throat opening) cut as low as possible on the CC and stay with the Pit Calc direction. This cut is as high as possible on the FB so then when I weld it to the CC the FB top is the top of the TO so then I extend the same elevation for the baffle plate (BP) through the CC. It is easy then to have about 4" from the BP to your bottom grate (BG).
jm2cw
Current Smokers: Backyard RF Offset and Hybrid RF Offset trailer rig with Cowboy cooker and fish fryer, always room for more........