  We investigate differential in-plane and out-of-plane flow observables in
heavy ion reactions at intermediate energies from $0.2\div 2$ AGeV within the
framework of relativistic BUU transport calculations. The mean field is based
on microscopic Dirac-Brueckner-Hartree-Fock (DBHF) calculations. We apply two
different sets of DBHF predictions, those of ter Haar and Malfliet and more
recent ones from the T\"ubingen group, which are similar in general but differ
in details. The latter DBHF calculations exclude spurious contributions from
the negative energy sector to the mean field which results in a slightly softer
equation of state and a less repulsive momentum dependence of the
nucleon-nucleus potential at high densities and high momenta. For the
application to heavy ion collisions in both cases non-equilibrium features of
the phase space are taken into account on the level of the effective
interaction. The systematic comparison to experimental data favours the less
repulsive and softer model. Relative to non-relativistic approaches one obtains
larger values of the effective nucleon mass. This produces a sufficient amount
of repulsion to describe the differential flow data reasonably well.
