Rear Slope Angle vs. Height Of Evaporator

Just thinking about improving my evaporator design for next year (as always).
Wondering what everyone else has for the angle and length of the slope inside their evaporator? (That pulls the smoke up and out and keep the air flowing.)
Right now our evaporator is made of stone and brick. The slope at the back is about 12" high by 20" long, and the evaporator is about 5' long in total.
Wondering what others have and their experiences. Should we make ours longer? Higher?
Interesting to see what everyone does! :D