This was my thought. It actually bothers me that Kias are very safe vehicles, as far as crash test ratings, side curtin airbags, etc. And there are no headrests in the middle of the back seat, and there are no rear facing tether locations. I am planning on keepong my son in a rear facing seat as long as possable just so I can fit my 3 kids in the back of my rio safetly.I never found an approved tether point for a rear-facing seat, so I used the metal base of the vehicle's seat to secure the tether as best as I could. Now that my son is forward facing it is tethered "correctly."
Always seemed odd to me that the ISO standard doesn't include a tether for rear-facing seats when it includes everything else and the manual specifies rear-facing.
To Funny. I actually have 2 Radians in there. I needed one to booster my 8 yr old in the middle because there is no headrest, (R120) and an RXT for the 1 yr old Rear faced on the passenger side. I still need to fit my 11yr old back there and that is the only way it was going to work.Not just the Rio. I have a Trailblazer and it doesn't have anchors for rear-facing car seats either. Feels like the industry/ISO forgot about rear-facing car seats.
If you are worried about space you can try the Radian r100 as it is supposed to be a thin-width car seat (Radian®R100 | Car Seats | Diono.com). I know the car seat I have hogs space in the back, although that is also because I have the 40 split seat folded down most of the time.