Ideally, the backrest is tilted back slightly, so when you turn the wheel your shoulders are the seat.
Ideally, the back of your car seat should reach the height of your shoulders.
Your shoulders should touch your seat when you turn your wheel. In order to achieve this, the backrest of your seat should be tilted back just slightly.
Your shoulders are not supposed to touch the backrest when driving. However, if they do it’s not a huge deal. You wouldn’t be arrested for it.