Hi thanks for the advice.
Yes on one of the building I have installed two AP in SE and SW around 4m above ground, with SE extend from SW AP.
I see some undesireable effect, the signal kind of bumping each other that cause some inteference in some part of the building. I use a signal range rule in capsman so if it is bad then kick the client and let the client choose next best signal.
While I can separate the channel, I need that feature for signal distinction between building, we have same 8 building like this adjacent to each other :(. And since I can only use 2.4Ghz ( many old device ) I only limited to 3 channel ( 1, 6 ,11 ) only, I think I'll reserve it for this.
This is why I try to put in the AP in West wall facing East, so as to not disturb the other building signal. The wall is shared and not that thick between building.
The above ground height is needed around 4m cause the West part is a tall door and I can only place it above the door.
Thats the theory though, I'll try to test it.
WiFi extension is not the greatest thing to do, if you can run wires. Quick advice.
I hope you adjust TX gain on APs. It is hard to say what is going on you premises, a proper spectral scan would be the best thing to identify issues, but if AP signal is issue then reduced gain will improve signal quality.
4m will be fine, most likely.