Should Caves have Fire-First or not?

[Poor Yorek]

Perhaps during the initial entry of the attacking unit into the cave hex (in game terms, the initial assault on the cave hex)? Perhaps this would simulate the initial difficult entry of the attacker into the mouth of the cave, whereas once that is accomplished (after the initial assault movement), the benefit of First Fire no longer attains?

Disclaimer: I don't have any of the PacFrnt games so I'm not familiar with the rules. This is therefore admittedly just an off-the-cuff thought.

PS. I suppose by extension, any time an assault is reinforced from outside, defenders would gain FF benefit (simulate difficulty in coordinating new forces entering the cave)? Again, thinking out loud here.