  We present a new paradigm for the simulation of arrays of Imaging Atmospheric
Cherenkov Telescopes (IACTs) which overcomes limitations of current approaches.
Up to now, all major IACT experiments rely on the same Monte-Carlo simulation
strategy, using predefined observation and instrument settings. Simulations
with varying parameters are generated to provide better estimates of the
Instrument Response Functions (IRFs) of different observations. However, a
large fraction of the simulation configuration remains preserved, leading to
complete negligence of all related influences. Additionally, the simulation
scheme relies on interpolations between different array configurations, which
are never fully reproducing the actual configuration for a given observation.
Interpolations are usually performed on zenith angles, off-axis angles, array
multiplicity, and the optical response of the instrument. With the advent of
hybrid systems consisting of a large number of IACTs with different sizes,
types, and camera configurations, the complexity of the interpolation and the
size of the phase space becomes increasingly prohibitive. Going beyond the
existing approaches, we introduce a new simulation and analysis concept which
takes into account the actual observation conditions as well as individual
telescope configurations of each observation run of a given data set. These
run-wise simulations (RWS) thus exhibit considerably reduced systematic
uncertainties compared to the existing approach, and are also more
computationally efficient and simple. The RWS framework has been implemented in
the H.E.S.S. software and tested, and is already being exploited in science
analysis.
