arch design/stack location

[Ryan August]

looking to upgrade next year. Some evaporators have the stove pipe coming out of the back and some come up from the back of the arch. I can rationalize a difference but anyone got something more than just guessing what the difference is. Is one better on an engineering or air flow or fire dynamics aspect than the other. Hmmmm.
thanks

[acerrubrum]

Last year I made an arch for my 2x4 pan. The arch is 5 ft. long and the stack comes out of the center top- right behind the rear of the pan. Now I wish I had the stack come off the rear/back of the arch and turn 90 degees and go up. With that design I'd have an area 12" by 24" behind my pans. Kind of a hot plate, that is hot as hell for pre-heater or something else.
Don't think that speaks to thermodynamics, but if I could design mine again I'd make better use of the area behind my pan.