Gas bills - the mysterious conversion factor

Hi,

I'm really curious to hear about other people's "conversion factor" or "common factor" that is applied to their gas bills. I'm starting to suspect that it is a major factor in bills, but one that is almost impossible to predict or control, particularly for those of us who live in apartments with centralised hot water systems.

You can read more about it here: http://jemena.com.au/Gas/Gas-and-you/Common-Factors.aspx

Our last apartment had a common factor of of between 0.24-0.30. Our new apartment has a significantly higher common factor of 0.37-0.41. So we are using the same amount of hot water but our bill has almost doubled. In fact, the AGL website says our last bill is more than triple the level of average similar homes - quite an effort for two people who have relatively short showers.

What type of common factor are others experiencing (it is listed as a "conversion factor" by AGL)?

Thanks.