It depends on the environment. AP225s have a downtilt omnidirectional pattern that allows you mount them high. If you have an 3.3 meter ceiling that is fine. Ultimately, you need to figure out how far apart to mount them, which is your next challenge.
For example, in an open environment like a warehouse, customers mount them AP225s at 10 meters height and at 33 meters apart, because RF propagates so far in open space. In an office environment, where there are alot of walls, you can mount it closer together.
The answer is, between 3 and 10 meters is fine, but you still would need to do a survey to figure out how far apart to mount them, based on RF propagation in that specific environment.