DirectX 11 games are still not properly scaled to fit the screen on lower resolutions than the built-in display's native (3200 x 1800). The game shows as centered. With Civilization V, the suggested circumvention of using the lower resolution on the desktop doesn't work. (Probable cause are the intro videos somehow resetting the screen resolution.) Only the DirectX 9 version (so happy there is such) of the game can run on full screen.
Also it seems that when using external display through HDMI, with DirectX 9 the computer gives the real resolution to the display and lets the display itself do the scaling to its native resolution (e.g. when running 1280x800 on display's native 1920x1200). But when using DirectX 11, the display adapter seems to put through the full native resolution to the display, i.e. scaling the image by itself before putting it to the HDMI. (The display's info screen shows what kind of resolution its input has.) I wonder if this is somehow related to the problem, (i.e. on DirectX 9 the built-in display handles the scaling (correctly), but on DirectX 11 the display adapter wants to do the scaling (which it does incorrectly).
My system: Lenovo Yoga 2 Pro, Core i7-4500U with 8 GB main memory. Display, as said above, 3200x1800 px. External display is HP lp2475w on 1920x1200. OS Windows 8.1 Update.
And BTW, could you please let the graphics control panel a) show itself in the language of my OS or b) let me choose the language by myself. Now it is showing everything in Finnish, even though all my settings in the OS indicate I want to use English. (I live in Finland.)