Effect of increasing the turnover frequency (ν_t) on ${\alpha }_{6\mathrm{GHz}}^{3\mathrm{GHz}}$. The solid lines are for a canonical α_nth = −0.8, with the blue line corresponding to a f_th = 0.1. The other lines shows the effect of increasing the f_th. The dashed lines are for the same range of f_th but with a more steep α_nth = −2. The dashed horizontal line shows a value of ${\alpha }_{6\mathrm{GHz}}^{3\mathrm{GHz}}=0$. This shows that we need FFA with a ν_t of ≳1.5 GHz to flatten ${\alpha }_{6\mathrm{GHz}}^{3\mathrm{GHz}}>0$.