Opportunity Fire Control

[Corto2London]

That depends on the scenario, or the task you have in mind for a unit.

In scenarios with difficult terrain, it might be helpful to keep your men and equipment concealed for as long as possible as the defender.

However, firing from close range also means the enemy fires from close range, which can make firing from range 1 worse for you than for the attacker if the attacker has more units or units with better quality and SA values.

Example: Guards Rifle units not in bunkers can't really deal with any kind of Panzergrenadier formation, as those will in most cases have an adjusted SA of 18.

Setting spotters to never fire will make them less likely to be discovered, particularly if you place them in a position where they can still see numerous hexes but are unlikely to be recon-spotted soon.

Units in ambush positions should either have opportunity fire set to off or not based on if they can and should start firing as soon as an enemy unit approaches. An example of this would be units in a town or forest, where the likely range of engagement is 1 hex. Do keep a close eye on elevation differences, to make sure they can actually only be engaged from the hexes you think they can be engaged from. The visible hexes function helps verify that.

OK, thanks a lot for your kind and long answer. 
But does it mean you adjust a particular Opportunity Fire depending of scenario, but you also adjust it in a game, depending of evolution of events ?