If you drive on these Fortress Walls, you drive in it, not on top of them.
That happens only, when you place the Object as a simple Object. {F71628}{F71630}
By walking on it, simple Object does not play any role.
These Walls are for Example:
Land_Fortress_01_10m_F, Land_Fortress_01_5m_F, Land_Fortress_01_outterCorner_90_F, Land_Fortress_01_d_L_F