The door can be tilted up or down in the front to back plane. This allows the back of the door to align better with the cab. This also affects the gap line at the cowl. It is a game of compromise to make it look right and allow the door to operate. If the door opening is a little small, the door can bind pretty easily. This is because the door edges and the door frames are shaped like a wedge. I believe this is a feature to make it difficult for a door to be knocked inward in a collision.
