If it's in the wall the difference will be negligible. These links should help.

Boggy on speaker location

https://www.gearslutz.com/board/bass...t-methods.html

How to find the listen position

https://www.gearslutz.com/board/show...99&postcount=6

Jens outlines basics of treatment including pictures, with links about resonators

https://www.gearslutz.com/board/show...0&postcount=11