Payloads have to be carefully balanced inside a fairing to prevent damaging and leaning the rocket askew during flight.
This might explain why SpaceX engineers will integrate the car front-up on its cone-shaped payload stand…
… Though it may just be for a better through-the-dash-window camera angle.
If successful, Musk’s car will be the first ever to fly free through the vacuum of space. It may also be one of humanity’s longest-lasting legacies in the solar system, since it’d survive indefinitely.