Yep, one perhaps counterintuitive thing is even when there is a flat level of noise across a 80 MHz of spectrum and a single client connecting when the client i

Yep, one perhaps counterintuitive thing is even when there is a flat level of noise across a 80 MHz of spectrum and a single client connecting when the client is connected at 20 MHz instead of 80 MHz the signal to noise ratio will be 4x better. There are other benefits to shrinking the bands as well, particularly because interference is rarely just flat across the entire band. The other big thing to do is disable the lowest basic data rates. Certain frames from the AP must always transmit at the lowest speed a client can be connected at and sometimes it's better to just let the client at the far edge lose connection than try to hold on to a poor connection at the detriment of everyone else with a good connection. Concepts like "airtime fairness" (or different jargon depending on the AP) also help prevent laggards from unduly tanking everyone.