The back rank belongs to the chariot
The deepest road for a chariot is the enemy's back rank — rank nine, the rank the general lives on. A chariot that sinks there (沉底车) attacks along the palace's own wall: the moment it checks, every king exit runs along the line it dominates, and the only answer is to stuff a defender into its path. Advisors pinned, forking threats everywhere, the whole camp budgeting moves for its own back line — that is the price of one quiet slide. Sink this one now, straight up the open a-file, with check.