"First tune your 5 GHz network, and then use your results to make an informed decision on how to set your 2.4 GHz power levels. The ultimate outcome will hopefully make your clients want to choose the 5 GHz network over the 2.4 GHz network (because of the superior throughput possibilities of 5 GHz).

 

Before I continue, note that each radio on each AP can be set to Auto (High), High, Medium, Low, and Custom. If you choose Custom, you can set an explicit dBm setting per radio.

 

First, you want to take the 2.4 GHz radios out of the picture by setting them to the lowest power possible. (This is something you would never do in a production network and is only done while you perform these surveys.) When all the 2.4 radios are at the minimum transmit power, walk to one of your APs. Stand underneath it and open a network scanner (like WifiMan or NetSpot) and see what the signal level is for one of your other APs.

 

If you can, as you stand there, flip to your UniFi app (or use a second device that can manage the UDM) and change the radio power for your other APs broadcasting your SSID to where their signal is -72 dBm or lower (meaning it should be a negative number of -72, -73, -85, etc). Keep checking your network scanner to see what the measured signal for the adjacent APs are. Eventually, you should reach a point from the perspective of standing under this AP where no other AP's 5 GHz signal is more powerful than -72 (meaning it's -71, -70, -58, etc).

 

Once you've completed this for the first AP, go stand under the next one and repeat the process so that none of your other 5 GHz AP radios deliver a signal greater than -72 dBm. Once done with the second AP, move to any other APs you have and repeat the process.

 

Regarding your three APs (including your UDM, if applicable)… eventually, you will have determined custom 5 GHz radio power settings for each AP.

 

THEN set your 2.4 GHz radio transmit power levels to be 7 dBM less than the 5 GHz levels you've set. So, imagine your determined 5 GHz TX power settings are… UDM: 17 dBM, AP1: 16, and AP2: 15… now imagine that you set your 2.4 GHz TX levels to the following: UDM: 10 dBm, AP1: 9 dBm, AP2: 8 dBm.

 

What's great about this is that you don't even need to worry about EIRP (which is the second number seen on each AP's Overview > Air Stats) because the measured signal at the neighboring AP takes everything into account.