Consider the following:
What caught my eye and inspired this post was a Chrysler 200 parked next to my rented Sonata in a parking lot in the Palm Springs area last month. The roof profiles looked strikingly similar, particularly where the roofline blends into the trunk area. Other details such as window shapes, metal sculpting patterns and so forth differed. That seems to be what stylists are allowed to work with these days, and not the basic shape of a car.
The Fusion's profile is also quite similar to those of the Sonata and 200.
Starting with the Impala, the next several examples feature a slight more dinct transition from the roof to the trunk.
Volvo often goes its own way, though not as strongly as its late Swedish friend SAAB. Here the roof-trunk blend is more an ogive curve than the other examples.