Do I read correctly that you put all the APs on the middle floor in a single line?
You should really spread the APs over the floors and as close to where the users are.
Cross floor coverage should be avoided (at least not relied on), and if you want to have coverage for the clients in the rooms you should really consider putting the APs in the rooms rather than in the corridors.
When APs have a direct line of sight, they will reduce power to prevent interference.