Tuning Intel MPI for Phi

Does setting

    I_MPI_MIC=enable

change other MPI environment variables, particularly any that would tune MPI for the MIC system architecture?  

As a side question, has anyone written a Tuning and Tweaking guide for IMPI for Phi?  For example, what I_MPI variables could one use to help tune an app targeting 480 ranks across 8 Phis?

Thanks

Ron