Radio size, D, in kiloparsecs as a function of the jet power, Q_jet, over the mean ICM density, ${\overline{\rho }}_{\mathrm{ICM}}$, for the group members of COSMOS (pentagons) and XMM-LSS (stars). The projected distance to the group centre in in kiloparsecs, normalised to r₂₀₀, is given by a colour scale. We plot dashed lines at constant t from Eq. (1) of Falle (1991), with values from Blundell & Rawlings (1999); Q_jet is normalised with the average ${\overline{\rho }}_{\mathrm{ICM}}$ of our samples. Solid lines denote the relation between size of the radio source and jet power, normalised with the median environmental density (10⁻²⁹ g/cm⁻³) from the MHD simulations of Vazza et al. (2023). We note the minimum Q_jet value used in the simulation is 3 × 10⁴³ erg/s, corresponding to X-axis values of 5 × 10⁴⁵ erg/s/cm⁻³, thus a simple extrapolation to lower values should be done with caution.