If you want to use the coordinate check method, you need to make sure that the box is aligned to the world, or you need to transform your check point so that it is in the coordinate space of the box.
An alternate, and more powerful, method involves doing point-plane tests with each of the faces in the box. I'd recommend this method if you ever intend on doing more complicated shapes.
An alternate, and more powerful, method involves doing point-plane tests with each of the faces in the box. I'd recommend this method if you ever intend on doing more complicated shapes.