If the exhaust is placed at the highest place in the cooking chamber, some fear the smoke will never get to the cooking grate. They believe (I'm one as well) the smoke will rise straight to the top of the cooking chamber when entering from the fire box, travel directly over to the exhaust pipe and out. This will also cause uneven temps along the grate. That is why you see tuning plates, baffles, or other mechanical devices being used to keep smoke on the food and temps evened out.
The couple of smokers I've helped to build have had the fire box entrance at the top of cooking chamber and the exhaust pipe inlet below the cooking grate (it was actually my dad's idea 25 or 30 years ago). This design keeps temps more even and ensures smoke to all parts of the chamber. Reverse flow designs essentially do the same thing. IMO, the closer to the cooking grate you have the inlet to the exhaust, the better the design. For me, below the grate is best.
Hope that long-winded response answers your question.