ITN: Is there "the one" answer to the question of how the contribution to management and overhead-costs is distributed among beneficiaries?

Unfortunately -NO. The distribution varies, depending on the set up of the project. It is about the consortium to decide. Usually beneficiaries which take up a lot of management tasks (for example, managing the whole training Programme) get a greater share. In general, the coordinator keeps a substantial share, especially when taking up the overall management of the project.