By setting physical_info none there is no BPI file that the game checks. The BPI files contains physical data about the boundaries of the buildings and probably things such as where soldiers can enter towers, stand on walls, but that is just speculation since BPI files cannot be modded at the moment.
Has this been solved ? is possible to make for example a curved shape for a bridge so that the soldiers rise over it instead of walking along it streight like they do normally?