Is contigency fee agreement are negotiable?

I'm a plaintiffs attorney in Mississippi and our contingency fee ranges from a third to 40%, depending on the nature of the case.  For example, for small car accident cases, our fee is usually a third.  For medical malpractice cases or cases that are more complicated, lengthy and/or expensive, our fee is usually 40%.   In addition to that fee, we also charge for expenses like postage, copying, legal research and the cost for obtaining medical records, etc.   If you signed a contract or agreement that referenced that fee, it is likely not negotiable.  However, you can always talk with your attorney and see if they are willing and/or able to reduce the fee any.