The issue of moving through gaps should be pretty simple - there are only 2 exceptions that allow you to move through a gap that is less than an element's width - given at the top of page 32 and i'm not going to re-type them here.
in hte case of hte expendables example asked about, the expendables are mounted so can interpenetrate the foot, so they can expand throug hthe gap (whether expendables should be able to interpenetrate foot may be arguable, but the rules allow it so they can)
As to the other question of whether expendables can expand from a column "as if by single element moves" - another thread has been raised...
see
http://dbmm.org.uk/forums/index.php?topic=443.msg2752#new
