It seems like a 1/2 run would be worth more than a 1/2 hit because going from 3.5 to 4 runs (for example) is a much bigger change than going from 8.5 to 9 hits.
it is based on what I have seen in sports books over the years. that's all I can go by. Maybe someone can give you a more official math formula, but that is what I have noticed.