Driver and port placement is very important if you are using the speaker for midrange or building a large box. Since you are building a large box you will have standing waves between top and bottom, possibly ruining your response.
I built something very much like your box,
Rebuilding a pair of srx. The box is basically a "-6 db bass shelf" as optimized by winisd. Placing the vent at the bottom allowed me to simulate in hornresp as an "offset driver". The box is a combination of BR and MLTL, the MLTL resonance filling in the dip in resonse curve around 100 Hz. Placing the driver in the middle of the box controls the first standing wave but the second at 300 Hz is impossible to avoid.
You can use Akabak if you have an old xp computer to simulate other driver and port placements.
If you want I can do a Hornresp simulation for you, since it is quite difficult to use before you learn it.