Well like the chart said, thats if it's a 50/50 spilt each time. And I don't remember that in the books, but it could be.

Even if it was 10% a time he would still be less then 53% (Harry having 6.48%) but I think what we have here this the almighty plot hole. JK might have written up to book 4 before she really worked out the soul spilting math.

But with plot holes it makes it for interesting fanfiction.