A basic hex in Advanced Squad Leader is 40 meters or roughly 131 feet. To put this in perspective, let us use something all of us (nearly all of us) are familiar with:
The above picture instantly defines the space within the hex. At first glance this may seem like more space then previously associated with an ASL hex. As you can see there is plenty of room within the enclosed hex to move which is interesting because movement only really occurs when one hex is left and another is entered. As such, perhaps this can explain a lot of the unexplained in relation to puzzling die rolls as deep within the unsimulated depths of ASL (and plenty of other tactical level games), troops aren't necessarily standing stone still until we "move" them to a new hex.
Spacial representation of a Soviet 6-2-8 squad's effective fire range.