Our base is set up in the middle. I figure a side collision could cause the most harm even if the seat is doing all it should.
We've given up on trying to fit the mirror in the best location.
I never though about who goes where when the next little peanut comes along.....

I must admit, the first time I heard the term "convertible car seat", I said to my wife "they make car seats just for convertibles???" At that time, I had a lot to learn :)