Using MPI to work with composed data-types, or data-types using pointers, is not a built-in operation. AutoMap and AutoLink are two tools that provide those functionalities to the MPI library, as a source-to-source compiler and as a subset of functions on top of MPI. Autolink uses buffering by packets to transfer more than one node of the data-structure it is traversing, in a time/communication efficient way. This "Packet" needs to be adapted to the system (cpu, network) used to be the most suitable possible.This article presents the "Fine Packet Tuning" tool developped to provide an easy way to do so.