The 26-year-old sits atop the table with 52 points to her name after three rounds as the race to reach Gothenburg in April heats up.
Usually, riders need around 40 points to qualify for the finals, with the reigning champion - in this case Adelinde Cornelissen - automatically guaranteed a place.
Truppa is followed by Swiss Marcela Krinke Susmelj, who has 45 points, 30 of which were won in Central European league competitions.
A quirk of the dressage competition's rules means that when the reigning champion scores points during the season, they do not claim them; in this way Truppa benefitted in Lyon, where she finished second but still collected 20 points because titleholder Cornelissen won the Freestyle Grand Prix.
In the Rolex FEI World Cup Jumping series, three riders have already secured their berth at the finals, to be held in Sweden from April 24 to 28 next year.
Reigning champion Rich Fellers, as in dressage, has automatically qualified, while Spaniard Sergio Alvarez Moya and Frenchman Kevin Staut have also made it as they top the standings on 58 points.
Behind them is Dutchman Jeroen Dubbeldam, who is in a good position after a flying start to the season which saw him win 35 points from the first two qualifiers.