Hello,
One question came in my mind, do we have on openwrt a wifi analyser that will give recommandion on WIFI TX power when you have multiple ap in your network ?
Ex: reduce power of this ap, change ap position...
No, there's no software that tells you how to adjust APs.
is this still state of the art, one year later?
Have ironed the firmware of my CPE210 with openWRT.
Remember they had some wireless surveillance in place.
Sad to have lost that 
Try this, AR signal mapper needs a decent phone.
In place of lowering power you can tune cell density that fisables low data rates effectively restricting it.