As long as it is installed correctly the seat is reclined more than it is sitting up.
Babys have more muscles than we think they do. By 2 months your baby is probibly trying to lift its head and is strengthening the back muscles even more.
If you are in an accident the injury rate of an infant and young baby would be worse if the child was laying flat compared to in a reclined rear facing position.
The forces that happen in a car going forward direction accident typically hold the child into the rear facing seat and the seat supports the head and spine. Where as if it was laying flat, that motion would wrench the baby in who knows what direction and the only support the child would recieve would be if it were a down ward crash... Like the car falling off something and landing on its wheels.
Where a rear accident (hitting something while going backwards or being rearended) The head would be supported in the initial impact and since your child would be strapped in correctly the body would be held immobile by the 5 point harness. (the first motion the head would make is towards the front of the car)
MUCH safer to have your child in a reclined rear facing infant seat.
FYI... This whole post is just what logic tells me. I have no actual scientific proof but you may probibly find some by checking out the internet resorces...