

There’s probably a bunch of reasons for the multi wing design, but the big one is going to be improving lift/carrying capacity without increasing the width.
The most efficient wings for low speeds are glider wings: as long and thin as possible. That makes them inconvenient to pack and folding joints are weak points. The second wing adds lift, but also problems: it’s less efficient than a single wing of the combined length would be and the front wing makes the rear wing less efficient. The winglet improves the situation somewhat. Facing downward also improves maneuverability.
You have to search using language that papers might actually use though. “Parachute effectiveness” means what the satirical paper is exploring, whether it prevents death or not. The only serious studies that might have used that language would be old WW2 studies that threw people out of planes with different parachutes to see how many survived.
If you want to know how to design an effective parachute, you should be looking at reference books like Parachute Recovery Systems instead.