Walls of gas turbine engine casings, fan cases, and methods for forming walls, e.g., fan case walls, are provided. For example, a wall comprises a plurality of composite plies arranged in a ply layup. The wall is annular and circumferentially segmented into a plurality of regions that include at least one first region and at least one second region. The ply layup in the first and second regions is different such that the ply layup is non-axisymmetric. An exemplary fan case comprises an annular inner shell, a filler layer, an annular back sheet, and an annular outer layer. The back sheet is circumferentially segmented into a plurality of regions, including at least one first region and at least one second region, and comprises a plurality of composite plies arranged in a ply layup that is different in the first and second regions such that the ply layup is non-axisymmetric.