Dependence of the σ_η parameter characterising the C2C variation in RRab stars on the pulsation period P₀ and the strength of the FM part of the Blazhko effect R. Based on the original O−C curves (left) and calculated from the residuals (right). Grey dots represent the sample of non-Blazhko stars from Benkő et al. (2025). Green lines show linear fits; r denotes the Pearson correlation coefficient. Red dots correspond to Kepler’s original targets, and blue rectangles correspond to background stars.