When using a rear facing car seat, be prepared for your child's legs to touch back of your vehicle seat quite early. (carseat.se)
Rear facing kids often have legs touching back of the vehicle seat. (carseat.se)
The rear - facing car seat's anti-rebound bar extends up toward the back of the vehicle seat and limits the amount of motion possible in case of an... MORE accident therefore decreasing the amount of motion for the baby's head and body. (thespruce.com)