I wanted to make sure just so I don't say, put your boostered child in the middle and there be just a lap belt (huge no!).
Any location in your vehicle sounds safe...especially with those side airbags.
If your are comfortable with the seating position now, then I would leave it as is b/c I bet seeing your siblings on either side of you keeps the baby quite entertained...LOL! You are correct, rear crashes, statistically, are much lower than frontal and side impact. I have had kiddos in my 3rd row and never thought about being in a rear crash.
I know I'm not much help, but I saw try out some different positions and stick with one that works for you! Good luck!