Wave Field Synthesis (WFS) aims at the reproduction of a desired target wavefront by driving an ideally continuous point source distribution with properly chosen secondary source driving signals. The backbone of WFS theory inherently relies on high‐frequency approximations. However, at low frequencies and critical geometries these approximations begin to break down, leading to performance limitations in practical implementations. In this work, we analyze the low-frequency limitations of WFS by focusing on the stationary phase approximation (SPA) applied to the Rayleigh integral, obtaining an analytical expression for the cutoff frequency that characterizes the validity boundary of the approximation. For a virtual point source, the derived cutoff frequency is shown to depend on the local curvatures of both the virtual source distribution and the Green's function, highlighting the critical role of geometry in 2.5D WFS configurations.