1. Cubeful 2-ply    13/7                         Eq.:  +0.1603
       0.5338 0.1557 0.0058 - 0.4662 0.1192 0.0026
        2-ply cubeful prune [world class]
    2. Cubeful 2-ply    6/4 6/2*                     Eq.:  +0.0941 ( -0.0662)
       0.5202 0.1576 0.0063 - 0.4798 0.1328 0.0041
        2-ply cubeful prune [world class]
    3. Cubeful 2-ply    20/14                        Eq.:  +0.0873 ( -0.0730)
       0.5270 0.1186 0.0038 - 0.4730 0.1206 0.0027
        2-ply cubeful prune [world class]

Not many builders to attack our back checker. So, improve front structure.