When filling your cakes, do you make the filling level with the top of the damn. If you don't will your top layer sink in the middle?
Fill it nearly full, but do not overfill. After you assemble and weight your cake, the dam bc will spread out if necessary for the top layer of cake to settle on the filling. After weighting, I square the sides of the cake with a sharp knife, trimming off any cake edge and any extra dam bc that's pushed out past the edge of the cake.