We chose the size of monomeric units and small ions within a range commonly used in coarse-grained simulations of similar systems. For instance, the authors of Ref. proposed a bottom-up coarse-graining of PAA from atomistic simulations, where distances between different carbon atoms between neighbouring PAA groups ranged from 0.250 nm to 0.450 nm. Herein, we chose σ mon ≈ 0.426nm = 1.20σ to represent an effective size of whole PAA monomeric unit, modeled by a single particle. For simplicity, we chose the same size for the polycation, using the monomer-monomer distance from the coarse-grained model of PAH proposed in Ref. For the size of the ions we used a slightly smaller value, σ = 0.355 nm, matching our previous work, 125 where we demonstrated, that this ion size reproduces the experimentally determined activity coefficients in aqueous solutions of NaCl, 130 in a broad range of concentrations, up to the solubility limit of c NaCl ≈ 700mmol/L.