i try to aim the speaker toward the middle of the opposite window area. ideally, imagine you sitting in your car, and project your shadow onto the window with a light, and put your finger on your chin, and move it out about 5" and down about 2"
where the tip of your fingers shadow is, is where i usually first test my image.
you can test your image by making the rear mould for the doorpod, and mount the baffle with hot-glue and dowels (i use chopsticks because they are teh free and easy to break lol) and then put the speakers in and actually listen to them like that. get some polyfill stuff and stuff the edges behind the speaker to absorb some of the rear wave. test several different aims.
honestly - every car is different. so you gotta actually hear it and listen to it for a long time in each way. and listen to alot of mucis, and try to pinpoint what you can realize changed.