Bellmouth Ports, the ports for Square vents

I just got done discussing with someone what i am doin with my wall in the car and have found a solution, a very cheap solution.

I need to have my wall flared on the inside and outside to try and achieve higher pressure levels.

My port area is 16.5" wide x 11.25" tall.

Look at the bottom pic to see what a Bellmouth port looks like- for my application -

There is a guy around town that can make me ANY custom size, flare, etc for my wall so i told him to hold off for a couple weeks while i test other things before i venture in flare port testing.

I have some questions though so i can get him to make the proper size.

The outside flare can stick out of the box a MAXIMUM of 5" deep. Any deeper and i'll void my division i wish to compete in.

So, how wide and tall should the flare end up being?

Internal is 16.5" wide x 11.25" I will be using either 0.5" or 0.75" thick wood so it will make the area a little smaller when the port is slid into place.

Now, onto the questions-

How much of an increase inch-wise should the outer flare be compared to the inner area?

If the inner area was- 15" x 9.75"... should the outer flare size be 25" x 19.75" is that too much, too little, how should i know???

how DEEP should the flare be? should the entire flare process be 2,3,4,5" deep?? how do i know?

Should the outer flare have a flat base by the time it's done flaring or not?

Can i just install damplifier pro to the outside of this type of port to kill resonance of the material or what should i use to be the most effective for practical use?

Any other things i should know?