I would recommend reading the 11ac rf roaming VRD. 

http://community.arubanetworks.com/t5/Validated-Reference-Design/RF-and-Roaming-Optimization-for-Aruba-802-11ac-Networks/ta-p/227716

 

For power, the default recommendations are:

    open office

          5 ghz   12 min 15 mx

          2.4       6 min 9 max

     walled office or classrooms

          5 ghz   15 min 18 max

          2.4 ghz   6 min 9 max

 

It also recommends turning off the lower beacon and transmit rates as well as a few other good tweaks.