[thatguy96]

HQ units are generally left out because of how SP handles small infantry formations. They tend to get knocked out quickly, and generally are of little use. What happens is that the remaining infantry squads are usually enlarged to a certain degree in order to make up for this lack of people. This is a convention that is consistant throughtout the OOBs.

A 6 man, non-scout unit is generally not the kind of thing most people find useful, nor have I heard of them making all the difference as you suggest. That's a speculative matter however, and I'm sure they have been instances.