Radian rearfacing

So. I have at the moment 4 car seats installed.
Will post pictures as soon as I am able, but I have a question. I read the manual, and it said for forward facing, the radian premier was until 53 inches, or until the top of the ear hit the top of the shell, with the harness coming out at or above the shoulder height. Great, no problem, and my oldest has hopefully quite a bit of time, since she doesn't hit the top slots yet.

But rearfacing just says harness at or below shoulder level with no height given.

RIght now we have 3 rearfacing in the back bench, two premiers and one radian 65, and one forward facing in the captains chair behind the driver.

The three in the back are the youngest, 1year + 23lbs 30 inches, 2 year 38lbs 37inches and 4 year old, 40 lbs and 40 inches. The 4 year old is on the second slots from the top, the two year old is on the third from the top and the one year old is on the third slots from the bottom.

How tall are kids allowed to be when rearfacing in the radian? All have tonne sof harness height but wondered if there was a so many inches below the shell rule or anything else?

Thanks for any help.

Most techs are comfortable with RFing until there is one inch of hard shell left above the child's head. I believe officially the RFing height limit on the Radian is 44".

Thanks. I just got off the phone with Shamma at SKJP, and she confirmed height limit rearfacing was 44inches(but not the shell above the head). Since I want to be safest rearfacing, I will take your recommendation to turn the 4 year old when their is less then an inch of shell above her. It feels so good to have the kids all in non crashed seats!