"makes more pressure in certain cabins.. not in all cabins is best to do the crx style."
True. And it's not just "Big SUV? port back, sub up." etc. either. It depends on the different models and furthermore the individual vehicle. Pete said he'd seen variations of +/- 2 dB with the exact same setup (not just done again but pulled right out of one car and into the other car of the same model) in different cars of the same model and year.
Remember that sound pressure and amplitude are different things too.
For us it is. Haha. Pete can model it and figure out the best way to do this but we don't have all the knowledge and home-made software he has. Gotta get back to researching.