I would recommend talking to a grant and contract administrator to find out how research works at Universities. Overhead is mainly used to support compliance offices at Universities. These are the people who make sure all laws are being followed when research is being conducted; (IRB, which deals with human subject research, IACUC, animal research, IBC, Biosafety, export control, and financial administration.) Research studies and travel cost for conferences are direct charges to research grants not overhead charges. Universities negotiated their IDC rates based upon a formula that the government created. The federal negotiated rate is only used when the funding mechanism a researcher is responding to indicates to use this rate. There are many funding mechanisms which use reduced rates or no IDC at all, which Universities accept all the time.