I have an iMac running at 1920x1080 resolution with a second monitor connected that is running 1920x1200 resolution. For reasons I won't get into, I occasionally need to enable "Mirror Displays" to show a single mirrored desktop on both monitors. I do this with the keyboard shortcut [Command–Brightness Down]. When I do so, OS X Yosemite 10.10.4 (14E46) will always set the resolution of both the second monitor and iMac screen to 1920x1200 because the "Optimize for" drop down menu under display preferences always defaults to the second monitor. Is it possible to default both the iMac and the second monitor to 1920x1080 when I enable display mirroring? Essentially, I want the "Optimize for" option to default to the iMac screen.