I believe the requirement on ground to beginning of wall minimimum is 1 foot.
Metal does not make them not rigid...the height, however, does.
Is this what you were thinking of?
Flood Insurance Manual - GR5
3. Solid Perimeter Foundation Walls
Solid perimeter foundation walls are used as a
means of elevating the building in A Zones and must
contain proper openings to allow for the unimpeded
flow of floodwaters more than 1 foot deep.
Solid perimeter foundation walls are not an
acceptable means of elevating buildings in