Melee modifier question

[LarkinVB]

Modifiers are applied to the melee strengths.
• If no attacking units have fired in that player’s turn, then 20% is added to the attacking strength.

We are playing PBEM with auto defensive fire. When does the above rule not trigger? Is there a case where a unit has fired and can attack in the same turn in the mode we play? You can only either attack in melee or fire afaik.