You might want to try an EFTA (Evenflo Triumph ADVANCE). It takes up less space, front to back, while rear-facing than most seats (including the Radian, and Fisher Price Safe Voyage Deluxe-Marathon clone). The Radian takes up the most space rf due to its height.
We have ours in the middle bench seat of our van (the short wheel base model) in the outboard position, and it leaves plenty of room for dh and I to drive (we're tall).
It will also fit your child at least as long as a MA, if not longer. The harness on the EFTA is 1/2" higher than the MA. My tall dd still fits the EFTA with just a bit of room left. RF to 35lbs, FF to 50lbs.
Good luck!