Jeremy, it's been done. That's for sure. And, iirc, it's better to do the burn tunnel tall and narrow, than shallow and wide. I have always heard that the burn tunnel should be the narrowest point in the whole system, if there is a point that has to be narrower.
Tho, it's better to keep the system size constant.
Making the burn tunnel narrow or wide has effects.
First, embers and fuel exposed.
If tall and narrow, less embers and fuel are exposed to air keeping the burn hot, but might have lots of excess air going over the burn.
Low and wide, more fuel is exposed, and embers too, to incoming air, which might cool off the fire too much.
Low and wide also has the tendency to block from embers accumulation.
Lately, i'm onto a batch and J mixture, in this case, it's real tall and real narrow.