Still learning after all these years...

[enrique]

For seven years I have played this way: a unit that entered an assault hex with entrenchment to reinforce the defenders benefited from negative modifiers of the entrenchment. I did not know the rule 12.41

Negative column modifiers for entrenchments only benefit defending units which occupied the entrenchments before the enemy units entered the hex.

and rule 12.43

If the hex contains defending units that are entrenched AND defending units which are not, the defending player may choose to take First Fire with only the units in the fortifications (the others don't fire), OR use all his units and resolve the assault simultaneously with the attacker.