how to design ports

Need more info. post all specs and plans that you have. There are to many variables to even coment with out more information.

I am afraid that I don’t understand what you mean by “dual diamond”. Is this what you mean?

a dual  diamond is where four sub will face each other ina a square config. slightly tillted of center. they all have a intersecting wave in the middle and it comes right out on your head. ive only done this with four or more fifteens so not to sure what it sound like w/ twelves it is used to create deeper and smoother bass.In case of snow drive backwards, instant front wheel drive, then again who needs it when you drive a Scoobie

Pointing the subs towards each other in that type of arrangement will not have any direct effect on the sound. The subs are to close together to each other to create any type of variation in response due to standing waves between the subs, and the opening is to large to make the space between the subs act as an independent resonating chamber. The subs will have a slightly increased output due to mono coupling but, this would also happen if the subs where all lined up on a flat surface and positioned close together. The advantages to a design like that is the fact that you might be able to squeeze all of those subs in your ride and it might be cosmetically pleasing.