Radius and diameter conventions in Köhler activation

Writing the same curve using diameter $D=2r$ changes its coefficients: $A_D=2A_r$ and $B_D=8B_r$ in $A_D/D-B_D/D^3$. The critical saturation ratio is unchanged, while $D_c=2r_c$. Mixing a diameter curvature coefficient with a radius solute term gives a spurious activation threshold.