It's rather late, but if I would do something, I'd do it in a different way. More simple, like this: for every stage you select X riders (let's say 3), and depending on their positions you get points (5 if one of your riders wins the stage, 3 for second or third place, 1 for fourth or fifth place for example). Same thing with GC: choose X riders and get points for their final position.
Nothing too complicated like stuff where a rider finishing 2nd is more favorable than a rider finishing 1st, because you predicted 2nd place.
Example: stage 1, I pick Sagan, Valverde and Anquetil. Anquetil wins (5 points), Sagan finishes 4th (1 point), Valverde finishes 7th (0 points) --> 6 points