In the HPS Early American Series & almost all game systems having advance-after combat and Zones-of-Control, there is a basic defensive doctrine which should be followed with virtually religious zeal. It is: the defensive line should be as straight as possible, running with the "grain" of the hex pattern, and there should be one vacant hex between each defensive position. (This only works when "weak zone of control" optional rule is not used.  If that rule is used the defensive line must be flexible and slowly recede for the tactic to be helpful.)
 
 
 
Optimum Defensive Line

 
The advantages of such an arrangement are these:
 
1. No unit can be surrounded when a part of such a defense (neither in the Enemy Movement Phase nor by advance after combat).
 
2. There are only two hexes from which any position in such a line may be attacked.
 
3. The line is the most economical use of units consistent with good defensive coverage.
 
4. If an Enemy unit succeeds in advancing into one of the positions in the line, it is relatively easy to counterattack such an exposed unit and regain the line (there is also a good chance that the advanced Enemy unit can be surrounded and destroyed).
 
 
 
 
The Least Desirable Defense

 

The least desirable defense is one in which there are two vacant hexes between each defensive position in the line. This type of line allows the units to be easily surrounded (by three or more attackers) and destroyed. Such a position is easily shattered and difficult to retake.

 
 
 
 
The Second Least Desirable Defense

 

 
 
It is also not desirable to defend in a "packed" line, i.e., one in which all of the defending units are adjacent to each other. This wastes units, and, more importantly, allows the attacker to make front-to-flank attacks.

 
 
Defending Against the Grain

 
 
When defending on a line situation against the grain of the hexagon grid, the units should be positioned in a manner similar to the optimum defense, i.e., with a single hex between each. Because of the geometry of the hex grid, the attacker will be able to attack any particular unit from three hexes.
 
As an alternative to a simple straight line against the grain, the player may wish to
"refuse" the flanks of every other unit, making these forward positions the strongest unit or stack of units. This makes the line strongest in the areas where the enemy can be the strongest (i.e., the only hexes against which three attacking groups can bear are those containing the strongest defending units).

 

 

 

 
Players should note that these defensive formations are idealized and do not take into account local terrain variations which may force upon the player less orthodox defensive deployments.

 

Source:  The Complete Wargames Handbook, 2nd Edition
 
Every Other Hex Defense