They bend their legs, like they do when they are sitting or playing or crawling into a box. My DD is 3 and will RF til she's 35 lbs unless she gets really uncomfortable, but at this rate, I see us turning her at the limit of the seat. It's no more less convenient for me to pass her a sippy cup over the back of her seat than it would be if she were FF. In fact, I might not be able to reach her if she were FF.
As DD got older I gave her more toys and I started giving her a "car bag" with some random toys and games that she could discover. She likes finding a book she hasn't seen in a while or a new dinosaur or whatever. We still talk, sing, etc. She'll point out things to me that she sees and if I see something interesting I'll say that there are "horses coming up on not-my side". She's in the middle so there is no "side" for her. She'll call out, "I see them! I see them, Mommy!" It's very cute.
So we'll keep her RF. That was what the technician suggested when we got her infant seat checked way back when.