Flank Morale Modifier

[BigDuke66]

Well that explains something, the rules used can have a lot impact on how a scenario plays out.
In turn gameplay the defensive fire is trigger or not, and even if triggered it is only 50% of what you get in the defensive fire phase. Less fire will lead to less casualties that will lead to less disruption and that will lead to less routs what overall makes the line too static.

Do you have the optional rule "Higher Fatigue Recovery" on? That one helps too to achieve lulls in the battle as the commanders take some hours to rest their units before engaging again.