To determine the composition of the coexisting phases, we expand on the approach used in our previous simulations of polyelectrolyte gels. 111,120,125 First, we select a supernatant phase of a given composition, and then try to identify, whether there could ) are snapshots of the three selected systems, using the same the color as in Figure . Green ticks mark a stable single-phase system, whereas red crosses mark systems with undesirable phase separation within the box.