Sometimes lag screws up the grid and pushes people in front/gives them a speed boost. All I know is that it is a fact that my Jaguar ALWAYS starts in first in PP700 races with its measly 619 PP, the only time that doesnt happen is when a Cappucino or something joins the race.
Its the very reason that people tune to 1 or 2 points below the PP limit, so they get a better starting position. 2 horsepower or 2% in weight is nothing in a trade for starting ahead of the pack for some people.