I concur with Dave and Bel: the point is not it being in contact, but moving into a position where it would make FRESH contact OR a unit not giving way.
One note, if the stands "slide" 2 cm along A they will contact the rightmost stand to (IMO), which would allow A only moving the leftmost stand into contact too... but that is a minor detail!
ALSO NOTE:
the disengaging move during combat is a move which is actually done after each CR !
as part of the fase-end-actions AFTER combat there is a REFORM moment where all units that participated in combat can ""redress ranks/optimize position". I know a LOT of players tend to do those two in one go, during Combat, but that allows to some extend for some "wiggling"