New for 2018, the Model 3 is a compact sedan that is significantly narrower and shorter than the already tight-in-the-back-seat Model S. The center is quite narrow – especially given the fact that 2D & 2P’s buckles are rigid and flush with the seat cushion.
When installing a car seat in the center seat, the head restraint is kept all the way pushed down – and for forward-facing car seats the tether routes over 2C’s head restraint. When installing a forward-facing car seat in 2D or 2P, if it has a straight tether strap you route the tether strap around the head restraint on the side closest to the door where the child is sitting – and if it has a V-shaped tether strap, like on a Britax car seat or IMMI Go, the tether goes around the fixed head restraint in 2D or 2P. The Tesla manual calls the V-shaped tethers “dual strap” tethers.