According to the datasheet (http://www.aerohive.com/pdfs/Aerohive_Datasheet_AP121.pdf) it appears to me that the signal comes out in a spherical shape and thus the vertical and horizontal signals are about equal in strength. It will certainly reach 20ft to the ground unimpeded by anything. If it's in the center of the room, I would think the corners of a large room could be a problem, but that's going to depend a lot on what band, frequency, and settings you are using. To piggy back on this after looking at the data sheet, it appears that the signal go up as much as it goes down? Curious if a mounted on the ceiling of 1 story, how good the signal would be on the second story or how much interference it would give to another AP above it.