In these tests, as the target concentrations (0.5 M Acetone and 0.1 M Pyrimidine) are no longer sufficiently dilute to approximate the excess chemical potential using an infinitely dilute hydration free energy calculation, we require a rigorous parametrization of the excess chemical potential of these species at this specific concentration. A full discussion on this matter can be found in Section 2 of the SI. Using the same protocol as above, we decouple a molecule of acetone or pyrimidine from a box already containing 0.5 M or 0.1 M of acetone or pyrimidine respectively. Further, in order to fully control the concentration of our test systems, we must also perform GCNCMC moves of the water molecules in the box, and therefore we also parameterize the excess chemical potential of water in these two solutions, although we found that it does not differ from that of bulk water since it is still the dominant species in the solution.