What is considered to be a 'long' torso? Seats?

DS1 has always been either average or leggy as far as proportions go, so I don't have much experience with this...

DS2 seems to be very long in the torso. I might need to get a travel seat soon, so I tried him in a Scenera today. At almost 27 months, he only has 1/2", or at MOST 1", before he is even with the top slots. (He was not very cooperative.) He is 38" tall. He is using the second from the top slot rf in his Radian65. (He's above that slot when viewed from the height of the slot vs. from above, if that makes sense.) Is this an exceptionally long torso? I can't even remember how much ds1's torso growth slowed down as he got older, but I'm pretty sure it did. I have a Regent, but it expires when ds2 is (just) 5 1/2. I was thinking of selling it to help fund a frontier (which would be used as a booster for ds1 until ds2 is ff). I really want him to be harnessed until around age 6 or at least until 48". I might sell the Radian instead, once he is ff. I should probably hold on to the Regent for this kid, unless I could be fairly sure that the Radian would last him past 5 1/2.

For those of you who have had kids with long torsos, how old where they when they outgrew the standard 40/40 sized seats such as the scenera by height? Do you think I need to worry that ds2 might be on track to outgrow the harness of a seat such as the Radian or Frontier before age 5 or so?

Thanks for your help.

I consider my son long Torso'd because he is in 24 months and 2T in shirts and only 18 months in pants (And can sometimes fit into 12 months)

DD1 is long torsoed, 18.5" -19" at nearly six. She out grew the CS at 2y and the Dorel harnessed booster seat at 3y in height. That put her at 15.5" torso then.
If he stays on that curve then yeah, he'll out grow the Radian by about 5 1/2. Bethany had 1/2", maybe, when the Nautilus came out. She is over by close to an inch in the RN installed. She turns six years in two weeks.

Of course, kids are very unperdictable.

Gwen was long torsoed (Nora is even more so) and outgrew the Scenera RF (by height and weight at the same time) when she was 3yrs 4mos, I think. Luckily her legs have started to grow, but she's still at 5 years old wearing a size smaller in pants than in her shirts.

Now, Nora is almost 18months and nearing the 3rd slot on the Scenera for RF.

I have a VERY long-torsoed baby. She outgrew my old-style Scenera at 9 months. The new-style, with slightly taller shell and slots, she can still fit in JUST BARELY IF it is installed at 30 degrees (at 45 she has already outgrown it.) She uses a Boulevard and an Uptown for her travel seats currently, but she's only a few lbs. from outgrowing them by weight, so no clue what we're going to do then-- haul a 40 lb. RF seat along for her, I guess.

However, in an upright Radian (35 degrees or so) she still has plenty of room to grow RF. (In a fully reclined one, she is above the 4th slots; with it 10 degrees more upright she is only on the 3rd slots, with about 1/2 inch to go before going above.) I fully expect her to make it to 40 by height, and probably 45 by height. At that point we'll see where we are as far as whether she is booster age or not. If she is not, I do have SafeGuard Child Seats and soon a Regent-- but it's concievable even with her long torso she might make it to 45 lbs. and a good booster age RF in the Radian, and then not need a FF harnessed seat.