I don't believe an airlines' insurance premium moves that much on the experience level of its commanders. I was promoted with 2900 hrs tt along with many others (B737-800). If the ocst was linear then it would be utterly prohibitive to promote until you hit a target set by a person(s) in an office with a computer who thinks they have correctly assessed the risk. Which could be anywhere, and where on earth would they get the data to compute and how would they do it?
Although, maybe they can and do.