  Closed orbit feedback (COFB) systems used for the global orbit correction
rely on the pseudo-inversion of the orbit response matrix (ORM). A mismatch
between the model ORM used in the controller and the actual machine ORM can
affect the performance of the feedback system. In this paper, the typical
sources of such model mismatch such as acceleration ramp ORM variation,
intensity-dependent tune shift and beta beating are considered in simulation
studies. Their effect on the performance and the stability margins are
investigated for both the slow and fast regimes of a COFB system operation. The
spectral radius stability condition is utilized instead of the small gain
theorem to arrive at the theoretical limits of COFB stability and comparisons
with simulations for SIS18 of GSI and experiments at the Cooler synchrotron
(COSY) in the Forschungzentrum J\"ulich (FZJ) are also presented.
