Opportunity Fire

[BigDuke66]

I have the "feeling" that the opportunity fire is affected by the state the unit is in, so high fatigue, low ammo, disrupted, etc. makes a unit less likely to do opportunity fire. But as said it's just a feeling because the manual doesn't mention anything in that direction.
And besides that, it's typical to feel that opportunity fire never comes when you really need it, luck is a bitch and what a bitch she is.