He told me that there is no such a thing called successful formulation regarding the subject, it is all case by case. I do not think it is a very helpful answer, so......
I had an idea of back-calculating each owner's share using pre-IPO S-1 filing, but he discredited my thoughts by stating many things have changed between formation of the company and IPO, such as rounds of VCs, change of management. The bottom line answer is that there is no straight answer.