Mutuelle - Contributions

Hello,

I have a question concerning the mutuelles. As an independent, I am required to be affiliated with one and I have to pay quarterly contributions ("cotisations sociales", the amount based on previous income).

Now I have read adverts by one mutuelle saying "pay thirty per cent less contributions".

My understanding was that the contributions are set by law and that therefore every mutuelles would charge you the same in terms of contributions (NB I am talking about the social security charges, not the monthly contributions to your health insurance). Therefore, how can it be that you pay 30% less contributions with one mutuelle, compared with another? Or am I missing a point here?

Thanks for enlightening me.

A.L.