You reduced the pit lane speed at Silverstone to 60 km/h to avoid gaining an advantage on the last lap by entering the pit lane.
Your workaround DOESN'T WORK because I've been overtaken numerous times by taking shortcuts on the last lap.
My proposed solution to this problem, which has been present in F1 games for many years: The pit lane should be closed on the last lap, and attempting to enter the pit lane should result in a penalty (e.g., DSQ). Similarly, failing to use two different slick tire compounds in the race (in dry conditions) also results in a DSQ penalty. Then, the correct pit lane speed could be set to 80 km/h.
It's strange that no one has thought of this after all these years.