The Citroen AX has come up in our recent discussions. It has a sagging line at the base of the side glass.
In this case, the curve makes sense whereas it didn’t on the Mercedes E-class coupe or the Colt 1400 that started it all. I think the feature might be a very standard touch that, for a time, became one of those things a designer always does: link the side glass to the front windscreen.
Here it is with the sag removed somewhat. The line is horizontal from the A-pillar to the middle of the rear door.