A=Predefined port opening height (port square inches / port opening width)
B=A/2
C=Thickness of wood
D=B+C+F
E=B+C
F=(Port depth) - E

E+F=Port Depth

EXAMPLE:
100square inches x 15 inches deep
A=5.56inches (100/port opening width is 18inches)
B=2.75
C=0.75
D=14.25
E=3.53
F=11.47