A Question on Rain and Retreating Armies

[Cat]

My general impression from reading up on a number of Napoleonic campaigns is that rain gives an advantage to the retreating side.  Both sides are usually pretty worn out and hungry even before the battle starts, then exhausted after the battle.  The retreating side has a great incentive to get out of Dodge.  The victors are now exhausted, hungry, wet, and darkness is coming.

Après Quatre Bras, the French pursuit got big bonuses to their incentive rolls because of the little man in the funny hat directing personally.