GC,
Three points:
a) Columns and squares have two very different and separate results lines on the charge table. A win to cavalry vs. a column will see a rather dangerous melee situation for the column and if it loses badly it's dispersed. End-Ex!
Whereas squares are far more likely to drive off cavalry, indeed there's no melee situation whatsoever. The vast majority of results will see the square drive off the cavalry; the only other result is the square being crushed, if very, very unlucky or more likely is worn out, with high casualties, etc, and up against good quality cavalry such as heavies or lancers.
b) The modifier to a column does indeed represent the closing up of the ranks and presenting a more solid formation to oppose cavalry. Thus cavalry are less likely to close against a fresh, formed column, but of course, that's not guaranteed.....far better to be in square!
c) The rules are designed to "encourage" players not to charge cavalry at fresh infantry formations. Players will find cavalry has far more impact against worn or even slightly worn infantry. That's also the reason the Discipline Test stays for a column at the higher end of the volley results, (and halving and then rounding down any casualties caused). Its steady (and that's important) infantry delivering a sharp volley as the cavalry close, but heaven help your infantry if they are worn, holding casualties or unformed!
Hope that helps.
DB