"If you allow columns to break up into separate columns, what is to stop a column of 6 LH(S) in the open splitting up into three columns to attack one enemy and get 2 overlaps?"
The difference is, that 6 LH in the open all have the same move distance.
If a long column of warband leaves a wood then, say, the first 4 elements could move 160p and are in column in the open
The remainer move only 80p, remain in the wood and are also in column, it´s just a second column.
So all of the impetuous troops have moved in column(s).
I find it a strange concept that impetuous troops should wait for troops further behind; it´s not what I see on the motorway when the cars exit the roadworks (,-)
("slow down dear, we´re leaving those poor people behind...")
I even had a look online for videos of troops wading but found very little:
At 1 min 25 this shows Americans wading. The first guys across do not wait, they move on fast.
http://www.criticalpast.com/video/65675057849_35th-Division-320th-Infantry-Regiment_soldiers-wade_smoke-rises_machine-guns-fired