Hello, from attached picture it is more clear.
1. you aim the signal to opposite direction. Behind AP there is some signal, but you completely send all power into the wall. It is logicaly too close. The best signal is in front of the AP and all around AP. Please see in AP package (box) coverage document where very nice scheme is drawn. Or it can be downloaded from the web (it is quickstart guide)
Try one or two APs on the ceiling with LEDs oriented along the center of the doorway. So horizontal orientation. I think that signal will be better.
2. Second - you are unlucky little bit because the room disposition can be WIFI unfriendly. It has two separated rooms (toilet and bathroom), so passing thru two walls required (one big from concrete and all other possibly from something more wifi friendly - like a plasterboard, or smaller bricks. And If doors are antifire with some iron or something like this, this can be the real cause with very difficult solution.
You cannot get from AP more power because you are limited by goverment regulation. Power maximums are defined by Country selection.
Advices:
Try different orientation and location for AP, best possible will be on the opposite side with front part with leds facing to the opposite door wall into the rooms. You will have more space to wide signal into the area. But try also the horizontal orientation on the ceiling.
But I am optimist it must have solution.
All other advices (Distance between APs, channel magic) are connected mainly to interferences. So if you say that no wifi exist in close area this can improve the signal very small.
You can improve signal using external antennas with MSM466 or MSM425. Or as i wrote before you can use MSM517 as replacement of data outlet but this means 90 APs into each room.