The non-reciprocal response of high-performance fiber optic parametric amplifiers was investigated. This response is attributed to the combination of fibers' inhomogeneous nature and their operation at deep saturation, but it is not clear whether this effect is promoted by polarization or dispersion. We show that nonreciprocal behavior is dominated by the fiber's local dispersion. Additionally, a simulation strategy capable of capturing fiber optic parametric amplifiers' non-reciprocal response is demonstrated.