  The GN model of non-linear fiber propagation has been shown to overestimate
the variance of non-linearity due to the signal Gaussianity approximation,
leading to maximum reach predictions for realistic optical systems which may be
pessimistic by about 5% to 15%, depending on fiber type and system set-up.
Analytical corrections have been proposed, which however substantially increase
the model complexity. In this paper we provide a simple closed-form GN model
correction formula, derived from the EGN model, which we show to be quite
effective in correcting for the GN model tendency to overestimate
non-linearity. The formula also permits to clearly identify the correction
dependence on key system parameters, such as span length and loss.
