I never thought about her legs as I'm just assuming she'll sit cross legged like Evan does in his seat, lol. He never has his legs dangle.
My kids have short legs so the leg support complaints others have had, we don't have a problem w/.
I think about legs because Ruthie doesn't like crossing them... it's good for her... the orthopedist AND podiatrist said it would help the muscles on the outer leg and help her start turning out (or heck, just straight would be enough for me) more... but, especially in the car, she really hates doing it (she has to in school both for compliance... at circle time/other carpet times where they do group activities... as well as so others behind her can see over her head... so she's not a good 3" taller because she's sitting on her knees, as well as because sitting in a W is bad for the spine and her legs/feet)... it's one reason I got her the Vivo... over the turbo... and it's why I ruled out using the Nauti as a booster (she would slouch to make her legs comfy)
She prefers a shallow seat where she can then pull her legs up if she wants... and rest her heels (in the vivo, she can still have almost half her foot actually) on the vehicle seat in front of the booster... without moving her butt from proper placement.
If the armrests on her booster were longer, or if I pulled down the vehicle ones, I have no doubt she would do what she did up till she got booted from the Nautilus when she outgrew it... fling one or both legs over the armrests.
But I get what you mean... and I wouldn't have thought about the legs and that before Ruthie... the boys were just so compliant... couldn't have cared less about if their legs bent at the edge... they didn't cross them, but they didn't complain or care, either... but as they've gotten older and I noticed how comfortable it was to have the room to cross or to have them bend naturally (and of course, not knowing if your kids were leg crossers, I mentioned it), I tend to think about making sure that kids can have their legs comfortable in a seat so they won't slouch (with boosters, I'm basically doing a 5-step test in them like I would with a vehicle seat... because hey... it's basically the same thing... seatbelt fit and seat fit)