I can only suggest you visit the ZIO website to find out your total contributions and where you've invested your money into (investment strategy-you chose when you enrolled for ISP). What I do is check it most of the time and see whether I'm making money out of my present strategy in the short term. Then look at the options available on whether I can gain by changing it for the long term. This also shows me whether how much is the approximate value of my entire portfolio (Company contributions plus my additional contribution).
And by the way, your computation is based on those people who didn't get ISP (gratuity payment, based on EOSB without investing). As to the actual amount it varies I believe based on the additional contributions (5%, 10% or 15%) you have signed for and again the Investment Strategy you've chosen. But it would help a lot if you visit the website and from there you can print all your contributions plus the company's share and compare this to the actual value (surrender value) stated in your account.
Just my two cents. Hope this helps.