I think Reggio is a certified car seat tech- maybe bring her into the conversation?? Also the car seat blog forum might be a great place to pose this question. I do know that when I took my car seat safety course, the technician said her own daughter rode rear facing and was 3 or 4 (I can't remember) and that she never complained. But she also said she crossed her legs or put them straight up on the seat back. Knees to the chest sounds uncomfortable. I could be facing my child forward at that point.