Question about 1" rule for rear facing

Someone posted a similar question regarding ff and harness height a while back, and that got me thinking...

My 2-year-old is currently rear facing in a radian65. There is a huge difference between his seated height when I first put him in the seat vs. when he has "settled in" the seat. When I first put him in the seat, he is sitting up straight with his back against the seat back. His shoulders are a good 1-1 1/2 inches above the second from the top harness slots. After he has been sitting in the seat for a while, he is more like at or a little above the second from the top slots. It makes that much of a difference! When I measure 1" from the top of the shell, do I go by the initial measurement or the measurement after he has been sitting for a while? I assume I would go by the initial measurement to be on the safe side? I know he's still got some room right now, but he is due for a growth spurt one of these months. I'm also wondering if it is worth it to consider a radian 80sl for him, but my thought is that he will be getting too tall to rear face in a radian anyway by the time he hits 40 lbs. (If measuring when I first put him in the seat, and assuming no huge jumps in weight before he grows taller.) Right now, he has a seated height of 24", a shoulder height of 15".

Thanks for your help.

Well, if you have a radian 65 that has the 40 pound rf limit, like it looks like you do, the 65 sl won't give you any more weight, as it still only rf to 40 pounds. Only the 80sl and the xtsl rf to 45 pounds. As far as initial height, and settled height, I have no clue

Jennifer mom to my 7 said:

Well, if you have a radian 65 that has the 40 pound rf limit, like it looks like you do, the 65 sl won't give you any more weight, as it still only rf to 40 pounds.

Click to expand...

Thanks for pointing that out. I didn't catch that. It would be the 80sl, then. I made the correction in my original post.