You can mount it in the wall or ceiling. You use the same bracket, and anchor to wall or ceiling according to your surface. The radiation pattern will change. Depending on your room size / coverage area, this may or may not matter. For example, I have one in each classroom. Some are wall mounted and some are ceiling mounted. Due to the size of the classroom, coverage wise it makes no difference for our needs/use case.
Esteban J Nunez
School and Church
K-12 Education