This might be a very problematic setup.
Wifi transmission typically is up to 20dBm (100mWatt), while a reception of a signal above -30dBm (1 µWatt) will saturate the receiver for the whole frequency band.
We use to be at least 30cm away from the AP with client devices. And with the size of the 2.4GHz and the smaller 5 GHz antenna , the received signal at the client device is expected to be -30dBm and -36dBm. The battery powered client device only transmits at 12dBm or even less for a smartphone (to not heat up your brain).
Setting 2 or more AP's with TXpower of 20dBm at that 30cm distance will probably saturate the receiver (totally distorting the wifi signal for the whole band, so even if using different channels).
10 cm is very very close (15 cm is the safe distance for your body parts)
For AP's I'll recommend 1.5 meter distance between them. Actually you can see the signal strength received, in the operator interface. Good value is between -40dBm and -70dBm.
Some people killed my wifi infrastructure last summer , by using GL.inet travel routers which they put just next to the host AP. ("Hey the wifi speed is not good , lets get closer to the AP"). They ended up by having no wifi at all through their GL.inet routers.