Invasion for Two, Please

I observed today's FMOCR (as I have mentioned before, I really enjoy that quest).  The group was small but scrappy.  They made great progress, but unfortunately ran out of time.  I thought that an appropriate response would be to have the orga march upon the town.

I created a sizable invasion for the relatively small number of defenders.  Some stronger members of the party ran forward – separating from the main group – and were ambushed in Tanglewood and fell.  Some individuals left the main group to solo-rescue the fallens who in turn got ambushed and joined the fallens.

This intrigued me: why would a group leave the strength of the party and run ahead into danger?  Could it be the glorious call to battle and the wish to demonstrate one's bravery?  Or is it some deep-rooted rankwhore compulsion seeking to get some secretive vanqs?

Or is the answer simply an aversion to mobs?  Could it be that some people prefer to act in groups of two or three instead of a group of fifteen?

I'm now thinking a little differently on how I run invasions.  Perhaps I could try making some small-scale invasions for smaller groups of people and see how they go.  And I still need to be a little better on improvising stories on-the-fly.  I need me one of those generate-an-instant-adventure charts.