My house is roughly 3K square feet arranged as 3 floors, 2 plus a basement. The 3 APs are installed, 1 above the other in roughly the "center" of each floor,
and arrange RF wise to be on differing WiFi channels in both the 2.4 and 5GHz bands. Nope -- they are all on ch-6 (2.4) and ch-159 (5 Ghz) and set to auto.
Power is set to default on all three, but the AC HD must have a much more powerful amplifiers, as they are reporting an EiRP of 28dBm on the 2.4 GHz channels vs 18dBm on the AC Pros, similarly in the 5GHz band there is a 4dB delta between the HD and the 2 Pros.
This results in my tablet, which I use on the main floor, where the HD is, never dropping the HD, even when carried to the other floors. Yet the bulk of the WiFi devices that are permanently on each floor tend to be linked to the AP on their floor.
Interestingly, as the crow might fly, the two 2nd floor and main floor hot spots are probably very close to equidistant from the tablet at night when it goes upstairs, so there's probably no significant degradation in the signal as far as the tablet is concerned. Certainly not enough to make it "roam".
I can't see, with my configuration, any benefit to adjusting the power of the APs.
Perhaps if I was trying to share a channel, between two of them...but realistically, I doubt it would help much, might be worth futzing with in the 2.4GHz band though. Just to see if anything moves around.