Hi,
You seem to be missing the point of my example.
My example of the Audio and Mic set up in iChat was to illustrate that sometime it is crucial which order you do things.
From the Quote post:-
My scenario (similar to OP):
At work - MBP Retina connected to external LG IPS by thunderbolt, no mirroring and extended desktop, laptop set as primary display
I.e. laptop is running internal and external display and has not problems even when waking from sleep.
Then:-
At home - Connected to external Dell 4K by thunderbolt, laptop in clamshell mode (ie laptop closed)
There are two displays but the laptop is only really running one - the external when the computer is awake.
There is no info at this point about which order the screens/Displays are set up in Displays (System Preferences).
The presumption would be that the external display is only mirroring the internal (if it were On)
There is no info about the external's resolution and how close this is to the closed Clamshell Internal display.
SO the person did this:-
At work, mirroring is off. You can't change mirroring when in clamshell mode, so for this test at home I had both screens initially on. The first important step was to make the external Dell the primary monitor by moving the dock over.
Then:-
Second step was to turn on mirroring.
So the External Display is now lead monitor
It is now set to Mirroring which the extra info indicates was not On in the first place.
The Result
End result - for over a week, not a single window has moved off screen coming out of screen saver or sleep.
They go on to say:-
Side note, changing the settings in order seems to be important - when I tried setting mirror mode first but didn't change the primary monitor (which you can't do once mirroring is turned on)
If my use of a similar instance in another app was confusing I apologise.

8:03 pm Monday; August 15, 2016
iMac 2.5Ghz i5 2011 (El Capitan)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
iPhone and an iPad (2)