  We consider the impact of multi-parton interactions, colour reconnection and
hadronization on the modeling of vector boson fusion and vector boson
scattering (VBS) final states at the Large Hadron Collider (LHC). We
investigate how the variation of the model parameters, compatible with a
reasonable spread of predictions around typical tuning observables,
extrapolates into the VBS phase space. We study the implications of this
variation on the total uncertainty budget attached to realistic simulation of
the final states in current event generator predictions. We find that the
variations have a non-trivial phase space dependence and become comparable in
size to the perturbative uncertainties once next-to-leading order predictions
are combined with parton shower evolution.
