A pattern only needs to be made oversized to compensate for whichever shrinkage stage actually changes the final solid dimensions of the part, since liquid shrinkage and solidification shrinkage are already taken care of separately through proper risering and gating, not through the pattern size. Once the casting has fully solidified, it is still hot and continues to contract steadily as it cools further down to room temperature, and this last stage of contraction is what actually shrinks the outer dimensions the pattern must anticipate. So the shrinkage allowance on a pattern corresponds to the metal cooling as a solid from its freezing temperature down to room temperature.