The distance BETWEEN walls is also computed, exactly when the term has a precise meaning, and plausibly where, as in corners, it does not.
The multi-block grid
The distance from the wall
The distance between the walls
The distance-to-walls and distance-between-walls feature is UNIQUE to PHOENICS.
It is extensively exploited by HOTBOX, the special- purpose version of PHOENICS which is used for the simulation of electronics-cooling situations, where the space through which the air must flow is "cluttered" with solid objects.