In this work, we show how \( \pi^+ K_S \) femtoscopic correlations, recently reported by ALICE collaboration in \( pp \) collisions, can be well described taking into account relativistic corrections and using realistic \( \pi K \) interactions. These are obtained from a dispersive analysis of scattering data, which provides an accurate and model-independent description of the \( \kappa/K^*_0(700) \) resonance pole. The chiral symmetry suppression of the \( \pi K \) interactions at low energies and the non-ordinary features of the \( \kappa/K^*_0(700) \) seem to suggest that the \( \pi^+ K_S \) source radius might be surprisingly smaller than for other hadronic processes when using the standard and simple Lednicky-Lyuboshits factorization approximation.