Time-averaged diffusion coefficient as a function of the mixed mode density for different masses computed with Eq. (3) using α = 2 and D₀ = 50 cm² s⁻¹. The points correspond to the additional viscosities estimated by Moyano et al. (2022) to reproduce the core-rotation rate of RGB stars at different mixed-mode densities. The red dashed line corresponds to a model where a constant value of D = 2 × 10⁴ cm² s⁻¹ was used until log g ≃ 3.9.