You’re welcome. I recommend that you search into review papers to get more accurate answers for questions like this. I haven’t worked in free-space-optics field, but I know one thing for sure: The reach depends on the atmospheric situation of the channel. For example, in free space you can have longer links with the desied reliability than other FSO channels. 2Km link is enough, if not too much. You might want to increase the number of the users instead.