Some things to concider are;
#1 - Flappers
My Brother scoffs at mine but I truly think they do help.
I glued a soda straw onto a piece of scrap carboard, bent 2 finish nails into a 90 degree angle and pushed the assembly into the foam.
And like this...
I am very pleased with such a simple addition.
Also, those Folgers containers are terriffic and free.
There was some discussion about having the intake high and the exhaust low, which is what I did. I think it only makes logical sense.