Why is the speed drop on Ubiquiti UniFi AP LR Access Daughters?

Question

Computer networks

I ask you to dispel doubts or correct.
We have Ubiquiti UniFi AP LR. Includes 3 plates. One from the Mikrotik is connected via a cable, the rest through the air to it. We have a comparative drop in speed on those two others. Channel 6, power at maximum. Distance 1 m (we test on the stand). This is fine? Or is it the cost of working all three on one channel or the cost of communication over the air?
After 2 years, AP LR was thrown out, 3 mikrotiks were installed, configured with the help of Which mikrotik can be selected for wide Wi-Fi coverage?

Answer 1

How busy is the broadcast? Maybe there are other networks on the same or neighboring channels that interfere?

Answer 2

On "myself" was loaded.

Answer 3

the rest by air to her.

You, I hope, guessed to dock them at 5 GHz, and leave only 2.4 GHz for clients?
True, a load-bearing (probably reinforced concrete) wall will be a big problem.

Answer 4

and by the way, can I have a prooflink about working in the “everyone-on-the-channel-shut-up-I-say” mode? I honestly do not know how to formulate a request to Google.