The above link (as of when this post was drafted) notes that the J30 was a mid-size car with the carrying capacity of a smaller car abaft of the B-pillar. That seems about right, as the focus of this post is the J30s rear-end styling.
By the early 1990s, most new designs were tested in wind tunnels with results that have affected styling ever since. But to some degree it was still a transition period. The J30 has a soft, minimally-decorated appearance in line with the Oldsmobile Aurora (introduced for 1995) and the 1996 3rd-generation Ford Taurus. All three cars lacked built-in trunk lid air dams and had rear ends rounded-off to one degree or another (the Aurora least so, the J30 to the greatest extent).
Let's look at the J30.