Most insurance copmanies use different modelling techniques.... If you visit their website, you will find it calcuated/populated automatically - thats the auto system, you can also call an agent and then increase your IDV. Clearly IDV(Insured Declared Value) is something we decide, you hence could choose to have it reduced beyond the general calculations - thats the play these companies have! Go in for ICICI Lombard or TATA, they have a very robust claim processing system - i recently claimed an alloy and a tyre (ICICI Lombard) - it was smooth (not to mention i know a few guys there). Simply put go for the highest IDV and lowest premium, its always better safe than sorry!