Toward the end of the GTP and Group C era, the quest for downforce lead some teams to a double-wing setup. Jaguar, Toyota, Joest, Peugeot and many others ran short tails and double wings, usually with massive endplates. The large lower wing was just off the trailing edge of the deck and effectively functioned as an extension of the underbody diffuser tunnel system, while the upper wings tended to be more compact and run at shallower, less-drag-inducing angles.
[ various proto setups, half width ]
I wasn't sure how structurally stiff the gooseneck-plus rear mount would be, but the design re-working around the burly lower mount allowed for an additional beam toward the base of the rear bulkhead for a huge stiffness gain.
A shortened diffuser (to match the shorter rear bodywork) leads to a large lower rear wing. Combined with a small upper wing, the overall balance of the rear downforce is now lower to the ground compared to the original single high-mounted wing which seemed to create more pitch and roll when turning.