  We study the numerical solution of the quasi-static linear Biot's equations
solved iteratively by the fixed-stress splitting scheme. In each iteration the
mechanical and flow problems are decoupled, where the flow problem is solved by
keeping an artificial mean stress fixed. This introduces a numerical tuning
parameter which can be optimized. We investigate numerically the optimality of
the parameter and compare our results with physically and mathematically
motivated values from the literature, which commonly only depend on mechanical
material parameters. We demonstrate, that the optimal value of the tuning
parameter is also affected by the boundary conditions and material parameters
associated to the fluid flow problem suggesting the need for the integration of
those in further mathematical analyses optimizing the tuning parameter.
