Name  <CuboidTag.shrink_one_side[<location>]> 
Returns  CuboidTag 
Description  Shrinks the cuboid by the given amount in just one direction, and returns the changed cuboid.
If a coordinate is positive, it will shrink the high value. If it is negative, it will shrink the low value. Note that you can also specify a single number to expand all coordinates by the same amount (equivalent to specifying a location that is that value on X, Y, and Z). Inverted by CuboidTag.expand_one_side Not valid for multimember CuboidTags. If you shrink past the limits of the cuboid's size, the cuboid will flip and start expanding the opposite direction. 
Example 

Example 

Source  https://github.com/DenizenScript/Denizen/blob/dev/plugin/src/main/java/com/denizenscript/denizen/objects/CuboidTag.java#L1434 