I think centering in general is a difficult thing. I wanted to mount an AC indoor unit over a window. Now, do I mount it center to the wall or center to the window which slightlty offset the center of my wall? I made the call to center it based on my wall. Now, 2 out of the 5 people that have came to my room asked me about why my AC unit is off-center. For them center is relative to the window and discussing AC unit placement as a conversation starter is a good idea.