Not a good way to carry if you are going to be seated.
If you are seated and have to get to your weapon you have to lean forward to reach behind your back. This is hard to do quickly and if your attacker has his eye on you is a dead give away. (Emphasis on dead)
If you are riding in a car the difficulties are multiplied by pretty much having to release your seat belt to get your hand on your weapon. If you have a gunman at your car window I dont think you will get the chance to upholster your weapon from this position.
If you are going to be seated I would recommend wearing your sidearm on your belt opposite your strong hand. This will give you the easiest access to the weapon from a seated position.
I’ve been reading about spinal injuries from the SOB carry. Rear end collisions or slipping on the ice can result in serious CNS damage.