Move diffusers (or keep extras) in 4' of water for winter aeration only, and the rest of the year, place diffusers in the deepest water. At a 4' depth, bottom disc diffusers will not be deep enough to do much to improve dissolved oxygen levels except under ice by keeping holes open.
If you have leaves entering, and do not break the thermocline, you are not adding oxygen at depth to support aerobic bacteria to speed detritus decay....and also oxygenating the 50% or so of your water volume below the thermocline in case of a failure.
It could take a couple weeks or so for the bottom water to become delpeted of O2 also, if there was a failure, and worst case scenario is, you have the same oxygenated volume as you do now, without aeration.
